Does this engine have narrow oil channels that can be blocked?
I flushed out thin flanes when I changed the engine oil (black paper thin & flat pieces. Probably soft and maybe soot) ..I wonder if it's enough to block any passages, PO had no spring under the oil filter. The second time I changed the motor oil it was "clean". I guess the black stuff doesn't block any passageIf someone used sealer on the base gasket it's quite possible to block oil flow to the head/cam. Other than that I don't think there's any real issue of passage blocking.