Vent above the seal.
There is a small triangular hole above the outputshaft seal that works as a breather hole for the swing arm.
Those holes can also cause gearbox oil to leak into the swing arm. The oil vapors causing the grease of the u-joint bearings to get thinner. Therefore not lubricating the U-joints like they should.
This same problem happens with drive shaft splines of the K75/100. But than its the leaking seal in the FD most of the time.(or gearbox)
The re-buildable shafts should be serviced every 10,000 km !! As was told to me by Mat from the Boxer Toko.
IMO Trying to get grease trough the grease point is tricky. As the grease is pushed trough it "should" lube all 4 bearings.
But I have often seen that the grease takes the easiest way out and will squirt out of 1 bearing. And its not going trough the other ones.
When those axles where new nobody could tell me what type of grease to use.
After asking a company how did nothing but re-building drive shafts, they gave me some grease that is so thick and sticky,
that it will never be possible to get it trough the holes into the bearings!!!
So every time I took it apart and stuffed the u-joint bearings and mounted everything again.
(i'm sorry I don't know what type of grease it was)
BMW R100'91/R80'93/R75/6 R80ST'83/R65GS'87/GasGasTXT300/DouglasW20-1920