I bought the bike at 10K in 2010. Since then, it has lived inside and been maintained as BMW directs by Ted Porter's Beemershop.
I rode to Death Valley last weekend. On Sunday morning, about five miles up the hill from Stovepipe Wells at 7:45 a.m., something let go in the drivetrain: felt like I was running over tar snakes (brrp, brrp, brrp, etc.). Bevel box wasn't leaking, and the rear wheel had no play on any axis. The wheel turned (noisily) in the correct direction, but would only go a bit in reverse before locking. The noise seemed to come from the driveshaft. The bike was ridden (very gently) down to the hill to Stovepipe, a better place to load it on the truck that had taken my friend's KTM dirt bike into the valley.
The bike went by truck back home, and this morning up to Ted's shop. Once the rear drive was removed from the swingarm, the problem was evident:
The u-joint was clearly deceased. I didn't see surface corrosion on the pieces, and Ted didn't think the joint had died from moisture. He said the pieces seemed (looked? smelled?) as though the joint had gotten extremely hot before it failed; he described a failure mode where the needle bearings get loose, and the moving bearing beats on the opening in the u-joint trunnions until the trunnion or the crosspiece fractures. This seemed a reasonable explanation of what I saw. As needle bearings live long lives in terrible conditions (open to the elements) in automobile driveshafts, this failure suggests BMW uses bearings bought to a price, not quality.
Fortunately, I'd stopped the bike quickly enough that the swingarm wasn't significantly damaged; there was only a small abrasion to the lip that retains the rubber bellows:
Ted says they see this failure on Hexheads often enough not to be surprised, and said he doesn't know if these failures are caused by more power, or cheaper bearings, or something else. In any event, this driveshaft is not repairable even if parts were available...and they're not. Instead, one must replace the whole driveshaft.
A new driveshaft is about $800. I've heard there was a running change in the driveshaft about 2009. Hoping that newer parts might be sturdier, and wanting to avoid the uncertainty of a used part, I'll spring for a new one.