Approx 500 miles after a Master BMW mechanic with years of airhead experience. All previous work he has performed on this bike have been without issues. (between 60,000 and 155,000 miles)

- replaced the clutch plate.
- rear main seal.
- pulled tranny - replaced major bearings and wear items in shift mechanism.
- other odds and ends that are not related to this problem.
After 400 + trouble free miles, I took the old gal out for 70 miles on a semi-pleasant January Saturday.
Returned home, parked the bike in the garage, warmed up with hot shower. Called it a day.

The following day, I went to the garage to plug in the trickle charger, and found a very large (and getting larger) puddle of either engine oil or 80/90 gear lube on the floor. It appeared to be coming from around the rear swingarm boot, where it attaches between swingarm and final drive.

The mechanic has asked me to return the bike to his shop, which I'll gladly do when we have a day over 40F, and no snow on the ground. In the meantime ........
a couple of questions:
- I can't tell from smell or feel whether the leak is engine oil or gear lube.
- I'd like your opinions on possible sources of such a large leak.
- Does the airhead have any breathers that could possibly clog up or fail, causing such a mess?
- Could engine oil (if rear main failed) make its way into the swing arm?
- Could tranny lube makes its way into the swingarm?
- Could final drive lube?
- Any possibility that the final drive seal(s) may have failed?

Since the shop will dismantle and repair, my questions are purely academic

Thanks in advance for any thoughts you can offer.