Perhaps you want t have a fiberglass guy evaluate the condition of your transom, there will be nominal fee.
Ask him if he can verify the transom is dry and not wet or rotted, and what would it cost to do such an evaluation. That you are concerned with safety of the boat. Ask a few shops the same and also ask what their experience is in Gradys, specifically.
I never read of a specific problem with a specific vintage Grady.
Grady screws up boats from time to time from a quality perspective, if it is a quality issue associated with not sealing the wood properly in the hull or transom, how you use the boat is not going to do anything to correct the problem. And once water enters, it can never leave or sry out by itself.
Quality screw-ups are more related to lack of quality contriol measures adequate enough to catch workers not following specs, taking short cuts, or leaving out entire build procedures when showing up for work on day after an all night bender.
I never read anything about Grady screw-ups being design related except on a few new models that Grady introduced, these design issues usually show up soon after purchase and reported to Grady. Sometime poor design issues are related to assembly specs setting up a worker to screw up, but here again didn't read much on this, if any it was minor.
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For different reasons, marine service mechanics as well as owners can screw up boats if installations involving penetrations into the transom or stringer grid are not sealed properly.
If someone wants to neutralize any possibe screw up at the factory, they would have to remove hundred of fasteners and the like into wood structures and reseal all over again with a proper procedure. If someone wants to assure professionals like mechanics and the like don't do the same, do it yourself, then you know it is done right.