I have a slow oil leak; the oil is dripping from the leading edge of the valve head cover, at the top right (pass. side) edge of the timing belt cover. The oil runs down the front edge of the block and onto the water pump.

It's as if something near the top timing belt pulley were leaking. (The plastic timing belt cover "ear" to which it bolts to the engine block is cracked there, but aren't they all...)

Any guesses as to what this is? The valve clearance was adjusted at 123K miles by a Volvo mechanic. Is a slow leak of this kind serious, or can it wait until the next timing belt service?

FYI, I checked the flame trap, related hoses, fitting on manifold, etc and all were clean and clear, so I don't suspect excessive crankcase pressure.

THANKS!