I thought this was a "snap"(shared) problem. While it has a similar result,the cause may be different.
To round off, someone painted my transom in 2 pack before my purchase(was the varnish bubbling?). It develops bubbles,and they contain liquid, ? water. Big task to take it back to teak after painting.
Now back to solving the OP`s question.
2005 Integrity 386 "Sojourn"