Ayiani: Welcome to the forum!
The Spirit 175 was our first Grady. About the most sea-worthy 17-footer you can get.
That said, the transom is solid, 1" thick wood inside that fiberglass. The question is whether anything around it has been compromised to let water in. Three places to look.
First, look carefully at the bang cap. That is the piece of aluminum corner brace that joins the hull to the liner at the transom. The engine mounting sits over the top of the aluminum brace. Still, you can see much of it. Look for such extensive corrosion that the hull-liner joint may be exposed and let moisture into the transom.
Grady has come up with a fix for this aluminum bang cap. Its a polyurethane piece. If you have a little moisture intrusion. its not too expensive of a fix - as boats go. If there is a lot of moisture, well you probably know it can get expensive quickly unless you can do it yourself.
The second area to look at are the two copper drain tubes that drain the engine motorwell. I bring this up because both of mine cracked when the boat was two years old. I noticed it right away. Grady replaced the tubes under warranty. they said it looked like one of their people squeezed way too hard on the tool that puts a lip on the tubes once they are in place. I don't think this is a common problem.
Lastly, any holes that previous owners drilled into the transom have to be suspect unless you can see adhesive sealant pouring out of the hole. I don't know a better way to determine of the transom has moisture issues than to have a marine surveyor check that out for you.
Maybe you can find one who is willing just to check moisture content at a much reduced price than a typical marine survey since this boat doesn't have the same systems on it as a larger cabin cruiser would have.
Good luck.
Rob