Ok let see where to begin,

I have a 2001 X5 3.0i w/sport package and cold weather package,Premium Package, pretty much every single option available in 2001 I bought it in 2003 as a lease return to dealer with 43000 miles on it, CPO covered it for two more years and/or 100K.

I live in CA with no real weather extremes so I can't argue with bashers who have owned an X5 in MINN or Maine, or some other GODFORSAKEN location on our continent with really cold weather and really hot weather, well now I live in Vegas the past 1year with my X5 and the temp. extremes for work so its not by choice and its a fun city to live in. I currently have 156K or so miles on my baby, she has some problems which I will detail for you but overall doing alot myself and few computer related repairs at a really good independent mechanic I would buy another one in a heartbeat if I had $60K to drop. which I dont....

THE ALL WHEEL DRIVE alone is worth the purchase better than others I have tried and I have the old version x drive

CV BOOTS are horrible especially in Vegas summers, dry and crack really fast about 2-3 years they go, so if you buy used make sure they do it and you inspect them before and after to make sure they were replaced the good part is the inner boots and rear inner/outer boots almost last forever, so the front outers are probably all you will ever have to worry about but its easy to do the inner boots once they take the wheels off so just have em all done.

ENGINE AIR HOSES:These were the tricky bastards, the hoses themselves are cheap, but getting to them without a lift is a pain in the arss, get those replaced all of them including the DISA VALVE the bladder in that sucker will set you back about $280 or so plus the other hoses so just get them all done at once its a $400-$600 job at any indy shop roughly if any unregulated air get in there the car will stall rough idle etc... save yourself the headache and youll be scotch free for almost 100K miles more, given the fact that SYNTHETIC oil is used on these engines internally they should look as good as the day they were made.

BELTS AND PULLEYS:I did this one myself saved myself about $500 in parts and labor, it was a pain getting the fan clutch off though, so have them replace the following, all 3 pulleys, the power steering,idler pulley and a/c pulley and upgrade them to the hydraulic versions if they dont already have them, I still use the mechanical pulleys since mine is 2001 and have them replace BOTH belts, A/C and Drive belt theres only two in the 3.0 which is the model I would buy over the crappy V8 4.0 versions. and Replace the fanclutch so you dont have to deal with it.

VALVE COVER GASKET: Git er dun, have it replaced as well and the sparkplugs it will be good for a long time and avoid messy oil leaks and burnt oil smell which I am about to do myself next week, gaskets should be soft and flexible they get dry and brittle but Ive never done mine and it has 156K or so, so this sucker has been good to me.

ALTERNATOR: Ohh man this one had me crappin my pants at first, I thought how in the hell did this part fail, well mine is a VALEO brand made in france and apparently thats the good one, the BOSCH ones tend to fail sooner, should have only lasted until about 100K mine lasted to 150K so no complaints there, I had alternator shop rebuild it for me only cost me $140 a new one from dealer or indy part store was between $300 and $500 and I did it myself so I saved 2 hours of labor roughly $200, had to remove the belts I mentioned earlier so I replaced those at the same time BAMM! Have them replace the alternator or be willing to jump in there and do it yourself its kind of fun to work on it. Makes you really feel good about whats happening under the hood when youve worked on things and know where the noises are coming from I can't explain it...

FUEL FILTER: BMW techs are really bad about replacing this part mines never been done and Im sure its over do, nor the indy or dealer has mentioned it probably because you have to remove a bunch of bolts towards the back and a protective cover and its a pain the butt without a lift, so I will probably have to do it myself, but its worth it to have done, and will save you an hour of labor and $80 for the filter and should be good for over 100K miles

OIL: I change the oil every 5K or so even though bmw recommends 10K my engine sounds great so 5K it is, no need to risk it, Im still smarter than all the dummies that change it every 3K and I use FULL Synthetic 5-30 doesnt matter which brand as long as you stay on FULL SYNTHETIC GOT IT!!!!!

INTAKE/EXHAUST CAMSHAFT POSITION SENSOR: doesnt take long get both of them replaced and it will save you a potential stall while your driving mine went bad at 80K or so no problems since took about 2hrs to change it and I worked real slow!!!

BRAKES: make sure you dont feel any shakes or vibration in the braking, if you do that means your rotors are warped dont settle for new pads, you can't turn or shouldnt turn german rotors because they are already thin, must be replaced so get slotted and some good pads and you should be in braking heaven.

AIR FILTER: spend $40 and buy the K&N Permanent Air filter its worth the boost in power and you can just wash it and clean it, will save you money on gas and replacing it.

SOLENOIDS:Have the tech plug in to the computer and reset all your computer controls for the windows, electronics, power options etc... you will thank me, for some reason they get stuck over time, power drain battery drain issues etc.... by reprogramming all of this it will refresh your old X5 to like new should do the trick, and have them update your engine software.

BATTERY: BMW batteries are expensive and dont last more than 2-3years max, just buy one at SAMS CLUB or COSTCO and save yourself like $100K that should be good.

TRANSMISSION: Okay I read a couple hater talking about how bad the tranny is, well not really, I mean the damn car weighs about 6000lbs so its a beast, heres what needs to be done, stay away from dealer have an indy reputable, replace the tranny filter and pan gasket and replace the connectors outside the tranny they tend to SWEAT over time and just need to be replaced after 100K or so, its not expensive and should be included in the tranny filter change, of course make sure the tranny oil is also replaced not reused, and this is most important, most x5 trannies fail because they are not recoded or reprogrammed correctly by the mechanic, they should plug it in for 1hour to the special BMW computer and recode the settings back to factory, people claim that for some reason after getting the filter changed and tranny oil changed they fail, I think the mechanics are to blame because they are LAZY and dont bother with the reprogramming part of the job. so you jump back in and drive like you did before and the shit hits the fan!!!!
IMO

Those are all the things I have run into with my 2001 x5 3.0i and when I hit the gas the engine still sounds smooth and sweet with KICK! just make sure you get a good deal get all these repairs bid out from a shop if they havent been done within 20K miles or so and find a happy middleground with the seller for price, and you wont be disappointed. Either hell sell to you or find a sucker to buy it as is but hes trying to make a buck to so maybe offer to split the cost towards the final price ????

MY RECOMMENDATION IS STAY AWAY FROM THE V-8 4.0 models, they SUCK!!! Serious, they are always in the shop, the engine vibrates alot more than the inline 6 all the parts are more expensive on the V-8s and I dont care what anyone else tell you contradicting that, you will end up emailing me "YOU WERE RIGHT" and all I can say is "I TOLD YA SO" get the 3.0 its decent power and gas mileage with smooth driving is in the middle 20s for me no joke and I have almost 160Kmiles on her.
:-)