I've been running Amsoil 20-50 in my R65LS since I had the cylinders off about 3K miles ago (63K on the clock). I probably should have replaced the rings, but the bores looked perfect, so I decided to leave well enough alone. The valve stems and guides were also within spec. The oil usage is about a quart in 2500 miles or so, which seems to me to be a lot, but there's no smoke in the exhaust, and the plugs are a nice tan color. Â The rear main seal eventually started weeping, and I replaced it with the new teflon style. Â It took me two tries to get it right - the procedure for the teflon seal is not the same as for the older style seals. Â Maxbmwmotorcycles in NH e-mailed me details of the install.
The oil pressure sending unit also started leaking about 500 miles ago. Â I don't know if the "creepiness" of the synthetic oil hastened either of these failures. Â Most likely it was just normal end-of-servicable-life stuff.
I put synthetic oils in the gearbox, final drive, and drive shaft, and the main seal around the output ring of the rear drive started to drip after a few hundred miles. Â A new seal cured that, but since then I've noticed a fair amount of migration out of the final drive all the way to the tranny. Â Someone on another Beemer site suggested simply draining the oil from the overfilled unit and pouring it back into the low reservoir, so I guess this isn't an unusual problem.
Other than that, everything seems ok.
Steve