[macojoe]

Well if you are getting movement then it is time to fix!!
You can drill a few 1/4 inch holes on the inside of the transome to see what comes out?? If dark dirt looking stuff comes out it is rot!! Just fill the hole back in with some epoxy after.
That motor if 390 # is alot of weight to be bouncing around when you trailer! If you don't fell safe about itthen I think you have answered your own question!! I no it sucks! But you have the hole season to fish! So you miss a little, better then getting killed over it! And if you go out with the transom falling off and you are just floating around in that cold water thats is just whats going to happen!!
That 73 has no floation in it so when it goes is gone!

Good Luck