Re: 1976 OMC Sterndrive motor mount issue
The two beams under the floor that run from the transom forward are called stringers.
Sort of like the frame rails on a truck.
So your boat kind of has a rotten "frame"
It's the whole backbone of the boat.
Hard to say the extent of the rot, but no way to tell without ripping up the floor. Could be minor.
Most likely major.
And the boat shouldn't be sold the way it is, except "as is" or "project condition" disclosed but that's your call of course
Yes OMC is out of business, and one of the toughest makes to support in old age, but Mercruiser and Volvo don't offer a ton of support for their 1976 models either... so if responding to that advice you got, you probably want something much newer.