I had a surveyor come and check out Blue J this week, after reading all these threads. Same diagnosis -- transom and aft starboard hull about to the water line. He checked the rest of the boat and found one stress point that needs immediate attention -- the starboard backstay chainplate mount. The rest, he advised, "just keeps water out" and should not stop
US Sailing this year, like Rhapsody.
He told me how to go about repairing the chainplate attachment -- I'll try to get pictures. Basically, there's a triangular plywood doubler glassed into the inside corner of the transom that has rotted. I don't remember seeing this particular item in any threads, but since this can only be inspected by removing the small bulkhead at the foot of the quarter berth, it may escape detection in many cases.
Looks like I'm in for some major work next fall.