Loose Lag Bolt = Rotten Stringers?

I am looking at an 87 direct drive boat with and Endmar 31and everything feels solid but some of the motor mounts are loose. 5 of the 8 vertical lag bolts for the motor mounts have no bight and are partially backed out. All of the horizontal lag bolts are tight. There is no evidence the motor has ever moved and it appears to be a lined. The boat runs fairly smooth and feels solid.

If you can take out several or all of the lag bolts (I would take them all out before I bought it) and take an ice pick and poke it in the wood it should not go into the wood more than maybe 1/4 to 3/8 inch. any other screws or bolts you can take out and check would also be good like fuel filter or blower attachment screws. If there is a ski pylon the attachment for that is another good place to check.

The stripped out lag bolts can certainly be an indication that the stringers have rotted, at least around the bolts.

If the rot is confined to just the immediate area of the bolt then you could get away with filling the existing bolt holes with "git-rot" or similar penetrating expoy and then changing/modifying the mounts so that the bolts are in a new location.

It is possible that a significant portion of the stringer is bad in which case you would be better off to find another boat.