I have a IO360 A1B6 200HP angle valve in my RV7. #1 has a crack in the head from the top spark plug hole. Engine has 700 hrs since rebuild, oil filter is clean-not making metal, cam looks good. My question is should I replace just the bad cylinder with a certified new cyl or is there rebuilt ones avail. or could/should replace all 4 with ECI expirimental cylinders. Where is the best place to get cylinders. Can I mix cert and exp cylinders. Any suggestions? Thanks