Agree with what others have posted - that cracking pattern is a tell tale sign of a wet transom and freeze/thaw. I had the same cracks appear on my 93 explorer a few years ago. See attached picture of the transom opened up. The entire transom is likely not wet, but there's enough to cause freeze/thaw cracking. Unless you get the moisture out it will continue. I don't have any experience with in-place treatments. I opted for replacement. I had mine done at Demelo's Fiberglass in Bristol, RI - Horacio does great work. He had 4 other 90's Grady's lined up for the same transom replacement. GW did a poor job with the 90's Grady's with the transom cutout and should have glassed and gelcoated the seam between the inner and outer hull. Through hull fittings are usually the other culprit. It doesn't necessarily mean the transom core is cracked as it's presenting on the gelcoat (that's the line of failure for the expansion cracking), but the transom is likely compromised and you may experience core failure at some point. It's common to replace them with coosa board now. I've seen prices in the $4k to $8k range. Wish the news was better.