First, check your oil level. If it is overfilled, this could be the cause of the leak. Overfilling can cause the oil to expand and come out of the vent tube.
Inspect your oil filter
Next, inspect your oil filter. If it is clogged, this can also cause a build-up of pressure and a leak. Remove the oil filter and inspect it for clogs. If it is clogged, replace it with a new one.
Vent tube is clogged
The vent tube might also be clogged. The oil that is leaking from the vent tube can be caused by a build-up of pressure inside the engine which can cause oil to leak out through the vent tube.
To fix this, remove the vent tube from the engine and inspect it for clogs. If it is clogged, clean it out and reinstall it.
Piston rings are worn
If the piston rings are worn, this can also cause oil to blow by the rings and into the crankcase. This oil can then come out of the vent tube. To fix this, you will need to replace the piston rings.
Cylinder is scored
If the cylinder is scored, it can also cause oil to leak into the crankcase. To fix this, you will need to have the cylinder honed or bored.
