1. During timing belt job, check also valve clearances ("lash"), all 8V engines have shims. No one does that. Plus, measure the camshaft lobes, the lift (no one cares about that too), they wear out. 2. Valve cover gasket and pseudo "o-rings". Check how the cover is contacting the head. Sometimes there is a gap from the factory, so o-rings will not hold the pressure long, oil will "flush" the o-rings. Spoiling the VVT operation.
