I have the 2.8 V6 12v and my #3 and #6 valves on the passanger sideis loosing compression and having blowby. I also can see oil coming thru a small hole on the pass. manifold pipe coming down in the pass. cat and that hole is leaking oil while the engine is running. How hard is it to replace the valve seals? Btw she has 219k on the orginal engine.