I've never seen one of those timing chain tensioners except on an OHC 4 cyl motor. Shouldn't be required on a V 8. How are the cam bearings? I think you need to disassemble and inspect the engine. There is a problem somewhere causing it to not seal up. May want to run compressed air into the spark plug hole, with that cyl on TDC firing , that will tell you where the leak is. Good luck!