This post is great btw. I too noticed my transom is rotting on one side only! This may be a real dumb question, but is it safe to replace just one side? It started with someone did not properly seal the TT exhaust plugs when they had OT headers. Plus the bilge dump was cracked and pumped alot of water into the transom The good part, the rot hasn't gotten to the stringers yet, nor near the pump housing, it goes from the RH TT exhaust hole up and right.
At first I thought it was my hose or the silicone leaking around the exhaust (I re-installed the TT). Then I noticed it would only happen when the boat got rocking in a lot of waves. The water would come in on that side through the seem.
Realy, jet boats don't even need wood. What does the transon support? A ski tow? 2 tie downs? It supports nothing but a housing to keep the water out, thats about it. It's all in the keel.