27' SeaMaster, Wood Stringer

[Brett]

I'm replacing the transom on a recently purchased 27' (Sea Mistress/Bleu Bayou) and need some additional info about the stringers. She had been converted to outboard bracket but the inside of the transom was completely rotten. It has some good glass under the rotten wood so I thought it would be a fairly straightforward repair. The glass under the p
outboard bracket is also fine. However, I can get my finger inside one of the stringers from the rear and it is also rotten. Looks like wood to me but it is just mush.

So, a few questions. Would a 1967 SeaMaster have wood stringers? What happens if I leave the stringer as is? Am I compromising the strength? Or what is the recommended repair? The deck is preventing me from accessing very far up the stringers. Should a drill a couple exploratory holes farther up? The deck is still in pretty good shape so I would hate to also have to rip that up as well. Wasn't expecting the rotten transom and would love to get some use out her.

Thanks, Brett