Yet Another Transom Job in the Works - ?ions

[motbed]

I bought a 73, 23 ft. Seacraft three years ago, had bottom paint soda blasted, repaired major blisters, barrier coated and painted bottom, sanded and powder coated windshield frame and replaced all class. This year I bought new repower package [350 mercruiser bravo one, mpi, seacore. My problem is after trying to install transom assembly I realized the transom was a little soft at one lower corner and was not able to torque nut to 25 ft.lbs.
Has anybody used gitrot in this situation or how should I repair the transom. After losing two summers, I hate to lose another.
Thanks for any information you can give me, Motbed