While you have things apart would be an excellent time to get inside of the transmission and find out if you have one of the infamous circlip transmissions.
You do NOT want to have your output shaft bearing to eat itself while in the middle of Central America.
The BMW airhead transmission is very reliable, except that for a couple of years they decided to remove the circlip from behind the large bearing on the output shaft. Nobody knows why...
What we DO know, is that the transmissions without the circlip have a nasty habit of eating that bearing because of the helical 5th gear pushing against it.
It is a relatively inexpensive fix, and afterwards you will never have a problem for at least the next 80-100k with regular oil changes.
It is probably time to have all the seals replaced anyway, and some of them are MUCH easier to do with the tranny taken apart...
For more information you can check out these two excellent websites:
I would recommend any Airhead rider bookmark the home pages for each of these websites if you don't already know about them...
Tom Cutter @ The Rubber Chicken Racing Garage does the circlip repair/installation on an exchange basis (shaft only) for only $66 including return shipping as of last month (when I had my new 1989 R100GS's tranny circlip done).
That is if you take the transmission apart yourself and just send the output shaft to him.
You can also send him the entire transmission and he will do the seals, inspect the bearings, do the circlip, and clean the whole thing up before putting it back together with correct shimming, etc...
Tom does quality work, and I have had a full transmission rebuild done by him, as well as the recent circlip install and other work.
Oh yeah, and get a LOUD ASS HORN!!!
(Steibel Nautilus is my current personal fave.)