If it has a motor mounted, you might be allowed to stand on the cavitation plate - use your weight to rock the transom. If it flexes its probably wet and will eventually need attention. You can also rap on it with a mallet or the like. Check for resonance variations in sound, much like when trying to find a stud on a wall. Best sound will likely come from areas that haven't been drilled near. If it has some screws in the transom, you might ask if you can remove a few and jam a twisted corner of paper towel in there to see how much moisture it absorbs. You can also get a moisture meter at a wood/hardware store and check the moisture that way. But face it - unless it is a virgin hull, there will be moisture within the transom. But I wouldn't call it a deal breaker.
Cracks along the top of the cutaway or the cap might hold clues of water intrusion, too.
Also push on the inside of the transom under the spashwell. Sometimes the woven roving there separates from the wood and that will almost always cause a bigger problem.
Eventually, transoms need to be replaced. The transom is cored with 2 sheets of 3/4" marine ply and wrapped in fiberglass, resin, and gelcoat. Once that exterior (or interior) coat is compromised, the water ingress will begin. Water will eventually rot wood and cause laminate separation. Any wood, on any boat. Consider this hull is 33 years old. You don't hear much about it with other boats because most people don't feel their "other" boat is worth the time or money to restore once it's 20 years old. Those other boats don't have a SeaCraft hull. Obviously you are interested in a SeaCraft, because either you've ridden in one and know the feel or are convinced that those that have, and do, do so with good reason.
My 72 Seafari has cracks in the top of the transom, exposed wood, and I've over-drilled & patched at least 30 holes from previous transducers, hoses, ladders, aux motor mounts and God knows what else. Most of those over-drills extracted moist mulch. But with a light old Merc 115, the transom is still stout and I probably won't touch it for another year or two when Pres. Obama's eco-groupies ban my 2 stroke.
Good luck. I hope she proves worthy!