A bit disappointed with having to rebuild my final drive about a month ago. Mileage, 39,700. The only symptoms were a slight oil leak and metal shavings in the gear oil. Turns out the crown bearing decided to start coming apart. Replaced the crown and tapered bearings, oil seal and o-ring. I decided to let my local BMW dealer do the work on this one. Total cost, $550. Of course, Labor was most of the cost.
I'm a bit concerned about the issues regarding the input shaft and clutch hub splines, but to date, I have no symptoms to indicate their is a problem so I think I'll ride it until something gives. The Dealer wants $1,625 to do a clutch service (new clutch hub) but that doesn't include the input shaft replacement if needed. If both are worn, both have to be replaced.
Chris at Affordable Beemer Repair (who many of you may be familiar with) offers a custom clutch hub that provides 100% engagement with the input shaft and solves the problem with the splines getting stripped out, as long as the wrench pays close attention to the clutch hub alignment procedures. Chris also highly recommends replacing the clutch slave while you're in there. Both custom pieces (clutch hub and slave) run about $725 shipped to your door.
I really don't want to get stranded somewhere in the middle of nowhere, so the options are to take my chances, or spend well over $2,000 for parts and labor to overcome bad BMW engineering and a mechanical problem that should have ended up as a recall.