Take the mast off the boat and submerse it in the lake (or a swimming pool). Look for air bubbles around the attachment of the sheave and top of the mast. A good whack on a Parking Lot will most likely loosen that connection and should be checked.
Don't wait to find out it's leaking the next time you tip it over, or it could fill up and pull the boat to turtle, then you've got big problems
...don't ask me how I know

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