I agree.

spoke too soon. Forward stringers are rot free. Transom was wet at the bottom so that will be replaced. Everything else is solid fresh rot free as I cut out large sections today.

I would agree that one that has been caulked after the fact, is possibly attempting to hide a problem .... If you are suggesting that anyone that uses caulk is amateur, Whatever you think ,chief. There are two ways to the other side of that tree. Glad you've had luck doing them dry.

Borgie ...What do you mean forward stringers. Do you mean the stringers get drier the farther forward of the transom you go? . Hope it all works out for you

How are the stringers forward of the bilge? Like in the cuddy, under cockpit, and bulkheads?

I agree motor. In fact I don't know how you would even keep the oring in place to install the transom assem without gluing it in place with chalk. I'd venture to say looking at borgies first pic of the flat oring and water marks on it, that if the original installer would have used a skim coat of 4200 or 5200 at install time borgie may not have a rotten transom now.

When your done repairing the transom take a wood filr and file a notch at the lower part of the hole cut out,,then apply some resin and may and glass around the whole cutout..then sand smooth and paint it with several scoats of paint,,this will ensure that water wont get into the transom again..do the same with the exhaust cut outs..

Absolutely correct. This will prevent water from collecting and sitting in those areas.

We switched to Life Seal on all our rigging a few years ago and no longer use 3M 4200/5200 unless we know without a doubt it will never need to come apart. As far as sealing a transom assembly, we replace the factory foam and use super weather strip adhesive from 3M to hold it in place. Then we have always used a sealer of some sort on the foam seal but now we use Life Seal never in an attempt to hide anything (as mentioned by others) just as a good sealing procedure that has worked for decades. Don't forget that most builders don't seal holes they drill in stringers or transom that always lead to rot..... time is money. Had the OP's boat been done this way when it was new he most likely would not have started this thread. We torque factory transoms to 25 lbs as suggested by Mercruiser, we torque our transom repairs to 35 Lbs.....because they are better than factory.

4200 will come apart ..5200 will probably assist in pulling the gellcoat off the boat if you have to take it back apart