hey guy,yesterday the mechanic've removed
the PCV valve.and also test the valve by used the mouth blow the air through the valve. sometimes the valve can hold the pressure sometimes it blow-by.So could it be the cause
of oil leak through the intake tract? today the new PCV valve will arrive.i will update later.

you mean sometimes this valve can hold pressure sometimes can blow-by.
it's quite weired from what i know that it should be able to hold the pressure all the time like when turbo boost up.the valve should be sealed,isn't it?
anything wrong pls corrected me.

It vents blowby gases back into the intake. Its a one way valve to keep humid air from entering the engine when its not in use.