The rear driveshaft attaches with a flex guibo. No need to touch it unless there was a separate fault there.

Having recently crack a transfer case, the output piece is isolated from the main part of the case. Unless something really bad happened, spline debris should be localized to the hollow part of the transfer case front output.

The people at Cobra a Transmission said they will not warranty their new shaft unless you also buy a new front output. If you are replacing the front output, you have to open the case and I would replace the chain and three main seals, too.

(Edited on 1/26/2015) Several sources for front driveshafts for the E53 X5.

You can buy the OEM shafts still(Part 26207508629 fits mine, confirm your model) lists now for $990 and can be found from online sources such as BMW Morristown for $708 but that still comes with short splines. You can also find used OEM shafts from wreckers (car-parts.com) for $150-$250 but those also have short splines.

Long splined sources:
1) Tom, [email protected], a member of this forum welds on a longer spline section and custom fits a new end to the driveshaft you send him. $525
2) Cobra Transmission sells all new units for $600. They also sell transfer case parts including a replacement female spline part for the front output of the NV125 tranfser case ($300 or so).

More iffy (to me) choices:

3) eBay seller rocketcoupe. Also seems to go by tcbmwx5. He sells shafts and the spline end you can have locally welded. He reported loosing a set of shafts in the mail around Christmas and cancelled my order with very short notice. He did refund my money and send me a weld end. Don't know what's happening now. About $165 plus $120 core.
4) eBay seller derwang. Something strange going on with tcbmwx5. No idea what is what. About $200.
5) eBay seller decom2011 - ships from Russia. $204 including 3-5 week shipping. $40 extra for fast shipping. Pictures look good. Don't know anything more.
6) Buy stub from one of guys above ($75-$85) and have it locally welded ($90-$160) if you can find a shop willing and capable. The first few shops I called insisted all BMW's need dealer only drive shafts and wouldn't even discuss.

Sounds like just using oem is faster and easier. Looks like you got 145k miles on your set- not bad I guess....

I wouldn't say that. Tom's and the cobra transmission front drive shaft seem reputable and have the longer splines. If you had the transfer case strip out like this thread, you have to do more than just replace the front drive shaft with another with short splines - it won't have anything to spline in to... If you are replacing a working shaft as preventative maintenance, than an OEM one could be an option.

The dealers usually suggest whole new transfer cases along with new front driveshaft to avoid this issue (nothing for the new shaft to catch on) which seems like overkill to me. If you really need the new internal transfer case parts, Cobra Transmission sells them (pre-xDrive which is the topic here) even what BMW does not supply.

Just received the drive shaft I sent to "The Driveshaft Shop" in North Carolina to weld and balance a longer spline. Here is what I received today.
$175 plus shipping both ways. I supplied the longer spline.

Keep me informed as to how it all goes back together for you. I am no expert by any means, but that looks like a rough weld to have shipped out. I am not trying to stir anything with my comment, will that interfere with reassembly at all?

Give yourself some expert points. (Sounds snarky, but meant as a compliment).

Ordered an all new shaft from Cobra today as I think I have run out of time and options.

Lol, hope it all works out soon. Working on ordering a new expansion tank... Fun never ends lol

to close this out. I've been in contact with the OP as he lived near me. He donated his X and didn't try to fix it.

My new Cobra Trans. front drive shaft will be going in this weekend in my X.

Good luck with everything.

On my 2001 3.0, about 20 months before I bought it last year, it was making clunking noises on acceleration. The PO had the dealer replace the transfer case (27-10-7-504-568) and transmission mount (22-31-6-754-088) for around $4000, but no change in driveshaft. It fixed the problem, but there was no specific diagnosis on what part of the transfer case failed. I don't know what the splines look like on the driveshaft.

I went in to that dealer recently and asked about this, and whether they considered an extended-spline driveshaft (since in all the other receipts it seems they were not shy about loading on extra repairs when they were doing one major one). Not surprisingly, neither the service advisor nor the parts counter people had any idea what I was talking about. They did have good free coffee though.

And as far as I know, BMW does not sell extended-spline driveshafts.

So does BMW not acknowledge this as a problem? Should I be concerned at all with the original shaft I have in there, and should I consider a pre-emptive spline extension repair to avoid future transfer case problems?

BMW does not seem to acknowledge the problem, but since there are at least 5 vendors selling some sort of extended spline driveshaft, it seems like a widespread problem.

I decided to replace mine when the noise started rather than wait. Getting stranded is no fun and can be dangerous. It's pretty easy to remove it and inspect the splines (undo the 6 bolts on the front guibo and slide the shaft out). Mine looked like they were about half sheared off. Perhaps seeing the condition will help you decide one way or the other.