Yep if you are in a damp climate as I am where condensation is a big problem, you really have to fog an engine left outside not used for 6 months. My yard equipment I keep garaged and in a shed so I don't have to fog them. When I took the old heads off I found two stuck valves.
Here's the interesting thing. Before the HGs blew, the last oil analysis I did in the fall showed a bit of salt (from cooling water) in the oil but very little. Well that spring, I heard a backfire thru the carb, when starting up, it ran a bit rough then smoothed out. I bet that was the beginning of the leaky head gaskets and may have caused some valve stem corrosion over the winter even tho it was fogged as usual. It ran fine, till I got water in a cyl at the end of Aug '16. But when I took it apart, very little corrosion anywhere. In this pic of the starboard head taken off, you can see one valve stuck open (its flipped around, the odd thing is the cyl what had water is the front one # 2, those valves were not stuck, it was the exhaust valve on #6. Just light rust in the combustion chamber of the head on #2, cyl walls and pistons were clean.
