I was sailing today then winds changed and motored about 45 minutes. The engine (Westerbeke 13 dieisel) ran great, normal temp and oil pressure. BUT, when I got back to the dock and was closing the thru hulls, I was shocked to see the entire area below engine and bilge were full of black oil. Dip stick was bone dry!!! I visually checked the engine and the only oil I could see on the outside of the engine was in the area from the oil filter and below. The Oil Filter was on tight. Nothing on the head gaskets or the outside of the oil pan. Rest of engine was clean! So I think I blew a seal around the filter??? Any ideas? No smoke noted and the engine had sounded normal. Again, temperature, RPMs and sound were normal. Anyone have thoughts? Could the engine have been badly damaged by brief but definate lack of oil? The access is nil/ lousy on the starboard/oil filter side. Any idea of repair cost? Thanks