I have a similar problem. After watching Steve’s video, I’m likely leaking from the o-ring around the pinion gear. In his video he shows a small hole than allows the final drive oil to pass through to lubricate that part of the driveshaft. Anyone replaced that seal? The Clymer manual says the final gear case disassembly requires special tools. Here’s his video:
Funny you mention those small holes.
UPS delivered my replacement unit with a damaged box. They dropped or mishandled it in shipment, then affixed a sticker saying they opened the box, inspected it for damage, found none, and resealed the box. The studs were protruding from the box on arrival. I have no idea how the could tell if it wasn't damaged internally. Only visible problem was the box and interior packaging were oil soaked.
So to check, I cleaned the unit, affixed some washers and nuts to the studs to simulate mounting on the bike, filled it with fresh gear oil, and tipped it up a bit (see photo). The holes on the shaft were originally up and down. After it dripped I turned the shaft 90 deg to see that the lower hole was filled with oil that wasn't there earlier. I surmised these were passage holes for the shaft or bearing lube. Clymer makes no mention of the holes.
After wiping up again, I set the unit level for an entire day with the holes horizontal and there were no more leaks. Figured all was well and good and mounted it up to the bike.
No idea when my next ride will be. I have the brake disk off the wheel and am waiting on wheel bearings to come in as a preemptive strike. I needed front wheel bearings this summer as I approached 100k miles, so replacing the rears seemed cheap and prudent at this point as long as the wheel was off. Also replacing the brake disk.
Scott