Here is my problem..I had my marina winterize my boat. After running the boat for the first time this year, in late April, for about 20 minutes total, I find milky oil. So, I ask the marina to 'check it out'. They proceed to tell me they think it's a "blown head gasket or cracked head" but didn't pressure check the manifolds, oil cooler, or closed cooling system!!!.. But, prior to me knowing, they proceeded to tear the engine apart - removing the exhaust manifolds, carb., distributor, heat exchanger, etc.. and they told me they had to do this as part of their diagnostic check!!!.. so, I have since terminated their service and now having my reputable shop work on it... As of now, they have pressure checked the oil cooler and manifolds - NO LEAKS. Pulled the heads and had them magnafluxed - NO CRACKS!..the head gaskets looked in good shape, and all pistons/plugs looked normal (no washing due to burning water)... SO, we are under the assumption it is a cracked block...but, will be pulling the remaining short block this week.. My question is, would insufficient antifreeze mix leading to a crack in the block over winter be the only cause of this crack??? The marina which did the winterizing has since told me they are not responsible because it isn't a winterizing issue, and it was my responsibility to ensure there was a sufficient antifreeze in the closed cooling system...and the crack is likely due to excess corrosion from not changing the antifreeze mix on a regular basis - - Is this all crap or a viable conclusion??? I have no idea what the 'mix' was in the closed system because I just bought the boat last July, and I don't know when the last time was the coolant was flushed and changed..... To, me it seems the mixture wasn't checked, therefore allowing a 'freeze' over winter resulting in a cracked block.....