The purpose of the PCV valve is to regulate the flow of crankcase fumes into the intake manifold where they can be burned. The PCV valve also has a secondary role as a check valve, to prevent flow back into the crankcase. This prevents potential ignition of the crankcase fumes, should the engine backfire. The PCV system is also crucial for to proper engine sealing. The system alleviates crankcase pressure, which can push out on seals and gaskets, contributing to oil leaks.

Oil in the breather filter may be a clue to gasket leaks in the crankcase or the presence of excessive blowby gases in the crankcase.

'Hope this helps...........