The splined driveshaft fits over the geared rearend drive & is immersed in 150cc of gear lube. The question is why?
I've wondered about this myself. Some years ago I had the universal joint on my R100 replaced with a Honda item (which is both fitted with a grease nipple and well sealed) due to the failure of the original and the fact that BMW do not recognize this as a repairable item and want you to buy a new shaft. Anyway, I was smart enough to slather grease into the spline coupling, but I didn't actually put any oil in the housing because I simply didn't realize that oil was supposed to go there (young didn't read manuals closely).
Exactly nothing bad happened.....
Some years later I went to a BMW club tech day and discovered there was supposed to be oil in there, so I put some in.
My wife's R65/80 has had a failed seal in the nose of the final drive for donkey's years - it is pointless putting oil in the shaft because it just migrates into the final drive and leaks out (assuming the final drive was filled to the original factory recommendation and not the later one.
The OEM universal joint from 1979 has yet to fail so I have my doubts that it needs splash lubrication, I harbour even greater doubts that it is even capable of being splash lubricated.
Yamaha, who largely copied the BMW shaft drive for the XS 750/850/1100 models ran the driveshaft dry, but used a very sticky Molly grease on the coupling.
Para-lever shaft housings with two universal joints are run dry.
I *think* that with lots of grease in the splined coupling that there is no reason the shaft cannot run "dry". I also think that the work involved in tipping 100ml (my "bet each way") of oil into the housing is neither here nor there.
