New Starter

So I left my boat at the dealership to get some minor things worked on (exhaust riser leaking and shaft packing). I have a 2000 mastercraft that is a DD, so by no means is the cover new. None the less when rain gets in it normally flows out the plug hole no issues. Well the dealership after lake testing it left the plug in for a week prior to getting around to working on it. During this week it rained a TON and the boat was pretty well full to the floor boards. Then when they finally did work on it they said starter was bad and want $395 to fix it. Do you think the starter going was from the water sitting in there for a week or just the age of the boat?