81 430 Xc Oil Leak

I have a new-to-me 81 430 XC. There is a steady flow of trans oil leaking from the fill cap while the bike is running. The overall condition is excellent. The fill plug looks to be original and the o-ring is new. I believe the bike was stored for several years. The oil level is correct according to the case markings. I have only run the bike for about 15 minutes as I would like to correct this issue. The engine compression is great and it absolutely rips. Is it normal for it to blow oil out until is reaches a "happy level"? The case vent is not plugged. I thought this might sound like crank seals need to be replaced. Any advise is greatly appreciated.

Nah they need to seal properly . The spinning of the primary gears throws it right at the cap . Do not open it with the bike running lol
The thread is very coarse and the face isn't flat play with 0 ring sizes or flat rubber washers until it behaves .
I settled on a thick o ring and less torque on the cap

Thank you silverstreakNZ. I'll mess around with various seals and o rings.

dont overlook the possibility of a dud seal. check for a huge cloud of smoke coming all the way from where you started. it will smell like burning gearbox oil...