Well my trans is toast... Seals are gone and when I pulled the drive last night the splines are looking really bad...

There is an ID badge on it that says:
Mercruiser Marine
Model number 400
Serial Number 6844291


So what do I need to search for to replace this thing....

Turbo probably has some used ones he'd sell for retail +10%

Isn't that an old TRS transmission?

Lol yeah i hear that...
I pulled the drive last night over at Sacket's place and well aparently driving in reverse for a weekend wasnt the best idea lol.

Most likely... The boat has speedmaster II's on it but I don't know what to search for on here or ebay...

I think that is pretty common stuff in there. I'd bet A & Red's could hook a brotha up.
And yes, driving in reverse was not a good idea. Those transmissions don't like to be loaded in reverse. That gear is meant for idle only from my understanding.

About all I can tell you is it's a 1984 MERCRUISER 400

I have drive shafts and carriers for those.

The splines inside the trans are toast the splines on the drive shaft are fine. The trans needed rebuilt anyway, I am just trying to weigh my options of buying a used one and having a spare to rebuild and put in when the other one does the same thing, or just rebuilding this one...

I guess what I want/need to know is are these the same as a Borg Warner 71c or 72c or any velvet drive trans or what...