Sounds like what happened to me. Full pressure 235 it started, ran fine and waited while I removed the many pounds of rust. After 1 year it started and was fine...then the water in the oil. Mine was a head gasket. Pulled the head, had it magnafluxed, checked for flat and true, And it was good. New head gasket and it has been good ever since. Why did it leak? I will probably never know. My leak was bad enough to raise the oil level on the dipstick after about 10 minutes running, I had 2 extra quarts in the pan. All water. Never happier to have not put antifreeze in an engine in my life. Still a habit from when I was just too broke to waste that stuff. Test with water, run with antifreeze. My best guess would be improper head bolt torque and sequence. I have not used "Seafoam" so no opinion there. Pull the pan and clean and dry it as best you can. Pull the head if you think the leak is at the head gasket. Get help with the head, it is heavy. Good a time to clean rockers, shaft and whatever you find. Keep everything in its' proper place. There several different rockers, so don't mix them. Pull the pushrods and keep them in order. I used a board with holes drilled for the parts. Labeled with a permanent marker to keep me straight.
