One thing I noticed when pulling the head bolts, other than one in the rear, none of them seemed to have any thread sealer. My understanding from what I read in "the book" is all of these bolts go into water jackets and are to have sealant on them.
Could coolant be pulled from the threads and into the cylinders?
BTW, this engine only has 5300 miles on it since being rebuilt. I put a 1000 on it (have receipts from PO).
