I have no idea why oil is leaking out of my GAS GAS' gear box breather pipe?

Ever since i opened the engine Oil has for some reason starting pushing its way out of the breather pipe on my GAS GAS. ive changed the gaskets and bearings inside and its STILL leaking. i have no idea what to do next....I have no idea why oil is leaking out of my GAS GAS' gear box breather pipe?
The most common cause is overfilling the engine with oil. More severe problems can be when engine compression is getting into the the gearbox and the pressure is pushing the oil out. That is usually from problems with the crank bearings or seals...I have no idea why oil is leaking out of my GAS GAS' gear box breather pipe?
That's why I take mine to my mechanic, cause working on engines is a tricky business. Gas Gas bikes, in general, have issues. I have seen 2 in my friends garage, both broken and only a few rides old.
Answer number one is correct, if it is over full then it will come out the vent tube. The only other alternative is that you have a crank seal that has either popped out, wasn't properly installed or has been compromised in some fashion such as it has a hole in it.
It sounds as the compression rings are weak and letting the motor to let the compreshem into the gear box pushing the oil out of the gear box.