Gearbox oil leaking through the vent

[gouna]

Good morning,
I'm French, sorry for my spelling.
My 325i has played very little for 4 years. I noticed a gearbox oil leak from the vent.
The vent was dirty and a little stuck, I was able to take it apart and clean it this winter. I drove 100km in January, I had no leaks.
Then the car remained at rest until yesterday, where I drove a little = the leak returned to the level of the vent on the top of the gearbox!
Do you have an idea to resolve this problem?
THANKS

[Brianmoooore]

Assuming this is a manual gearbox, are you sure it's engine or gearbox oil, and not brake/clutch fluid?

[paultv]

Doesn't this happen when internal pressure builds up in the box, because the vent is blocked?

Paul