Re: Wet Transom
A wet transom is when the wooden core becomes saturated with water. The wood delaminates and rots. I don't know of anything that will completely prevent it, but I can tell you some things that will guarantee problems.
A: Drilling holes through the transom and not sealing them before inserting the fastener. Do NOT use silicone to seal.
B: Keeping the bilge area wet or not allowing air movement when the boat is not in use.
C: Ignoring cracks in the transom area or splashwell, although if there are cracks a problem probably already exists.
This is not a comprehensive list, only the most common in my experience.
Repair involves surgery, you can browse the restoration threads for more input there.
Welcome Aboard and Good Luck.