Transmission oil leak

I have transmission oil leak between the "main drive gear" and "main shaft". All the seals are dry and most of the oil comes after a ride. One could think that the oil level is to high but it isn´t. When the bike is horisontal, there is no leak. The gear case is from 1947. Does anyone knows what causes this?

[Pa]

Did you wipe the case off to see where the oil originates from ? May be as simple as a gasket. May be a mounting stud. May be a hair line crack in the case. May be the drain plug. May be a seal even though you believe yours look dry. My suggestion..... Try doing the wipe down. Ride the bike until real warm. Park bike. Remove rear wheel drive chain. Run bike in gear and look for leak.

Greven,
Is your transmission vented correctly? If not when it is hot it will push oil out the path of least resistance, usually between the drive gear and mainshaft, or the kicker shaft.
Is your main gear the early type with no seal in the end? If so the only thing that prevents leakage is the fit and the reverse cut spiral in the bushing.
Robbie

Or just use liquid grease like most old pommy bikes used before real seals were used. Castrol spheerol! Lawnmower boxes use it too.