I am hoping for some advice on the next steps to take. At the end of last year, the engine overheated and the head gaskets failed. Replaced the head gaskets, new oil and filters and put new exhaust manifolds on (see this link, post 22 here: http://www.clubsearay.com/index.php?threads/8-1-low-oil-pressure.110903/page-2#post-1363938 for more details). Ran the engine for 8 hours over the winter since the repairs then changed and sampled the oil, and here is the report from Blackstone: If is seawater, then the likely culprit would be the oil cooler. but isn't the oil in the cooler at a higher pressure than seawater? Am I missing another source of seawater? If it is coolant, then either a gasket failed, or we missed a crack in the head, or the block is not happy. What is the best way to narrow this down?