If it had a fair amount of water in the oil your gonna have to change it several times to get the engine clean. When you had the pan off and pressure checked it the engine block was cold, when they heat up sometimes thats when these little leaks decide to open up. From what I've read you have two options : replace cylinder sleeve O ring and head gasket or put in Bars stop leak and run it. Pull the valve cover and see if there is a lot of white oilly stuff in there. If it has several hours on it , I'd pull the valve cover and check for moisture and clean it out , drop the pan and clean all that real well. Put in a cheap oil run it an hour or so , change it to a good oil put the Bars stop leak in run it like 4 hours to allow the sealer to work. And run it for 20 hours or so and keep an eye on it. If the problem persists its time to take it down.