I have 175 K miles on mine. It started the cold start grumble recently and rough idle a few years ago. I found a piece of timing chain plastic in the oil pan a few years ago. I have just started my timing chain guides and am in the process of disassembly. I decided to do mine now because I want to keep my X5. I have a 4.4 2000.

Definitely without a shadow of a doubt have the timing guides done now especially at that mileage. It's a ticking time bomb that will if you're unlucky take out your engine too when they go. My guides failed at 123k and I'm just recovering from the cost of doing everything. Luckily mine didnt take out the engine although it did have a knock on effect of collapsing a lifter 60 miles after I had it all back together again which was frustrating to say the least.

Not worth the risk at all.

Mine went out at 130K. Just got them replaced.

im awaiting my mechanic, to get the price for the work being done,
Richard is too scared to do them himself , and is out sourcing the work to an engine specialist
(he owns a mini garage, but is a BMW tech, (i think he doesn't have a hammer big enough to work on a x5 any more):)
im guessing 500 to 600 quid. and after talking to the wife yesterday, i think ive gone past the point of no return money wise, with this car, if i sold it , i would definitely be at a loss