Other than "Faulty Manufacturing" I can't explain what might've happened to Richard's driveshaft. As for the GS driveshaft failures, those began with the new generation of GS bikes. The added suspension travel and para-lever rear-drive setup apparently stresses the metal more than on the pure street bikes which don't get nearly as much off-road abuse. Still, replacing a driveshaft is a helluva lot more time consuming and expensive than replacing a chain. I have NO idea what goes through their engineers' minds any more. I gave up on the brand five years ago and wouldn't touch ANY new vehicle with that "Roundel" logo on it no matter how many wheels it has.
Many people these days believe BMW is living off the great reputation they had in the past.
I think part of the problem is BMW keeps on coming out with more and more models. Back in 1971, they basically only had three versions of the same bike and many of the parts were interchangeable between them. Any part needed, no matter what it was, was always in stock at the BMW shops.
And no matter what breaks, you usually could fix the bike on the side of the road. if you carry the right stuff (cables, etc.). BMWs came with a very good stock tool kit that could pretty much take the entire bike apart on the side of the road. Those days are long gone with the newer bikes.
Anyway, years pass and so all the old engineers who design the bikes are now long retired. So we can no longer expect much to be the same as it was back in the 70's.
It seems BMW discovered they can make more money with less reliability and bikes that are more difficult for the home mechanic to repair. But it is not only BMW. These days it's all about profits, they do not care about much else.
-Don- Reno, NV