no compression in 1 cylinder after winter

Question for the forum. I bought a boat with a mid 90's merc 2 stroke outboard last October. Compression was checked and very good in all 3 cylinder boat ran fine the few times prior to winter. I'm in Seattle area so the winter is pretty mild.. disconnected fuel line and ran it to empty prior to winter. stabilized fuel.. Fast forward 6 months and brought the boat in to a mechanic for a preseason tune up and I get news that only 2 of 3 cylinders have compression.. They are currently checking plugs and carbs . Any thoughts on what may have happened to cause this? Any input appreciated.. I'm new at this and trying not to go to the cleaners right off the bat.
Thanks in advance
ab

If that's an early Merc triple (50 to 70 hp), and it's the top cylinder, that's not uncommon. Of the dozen plus Merc triples to go through my shop, only one had a good top cylinder. And the damage happened long before you laid it up.

Sorry.

Jeff

Nothing can happen over the winter to lose compression.--------Get the boat and test compression yourself.-------Tester is in the order of $40 or so.