Poke around on the wood. If it's soft, or has soft spots it is most likely in need of replacement. You have a really good support brace built in and that helps alot. If your wood is not rotting/rotten, you should weather proof it as much as possible. Some boats are easy to replace the wood in the transom, others can be a completely overwhelming job to the layman. If you can remove the fasteners on your brace that are connected to the transom without tearing anything up, you could then just push and pull your transom to see if there is any flex or play. If there is, you may want to consider rebuilding it with a newer wood. The boat I am currently working on had it's transom covered by a sheet of aluminum on the inside and was tough to inspect. However, the previous owner had made a really bad attempt to repair it and chose to just add a 3/8" thick peice of aluminum plate to mount the 60hp Mariner onto. The transom had completely pulled away from the backwash pan allowing water to pour into the back of the boat upon stopping the boat. The fix was beyond his knowledge, which led to him GIVING the boat to a friend of mine just to get rid of it. Once I removed the interior aluminum, there was no question about my transom. viewtopic.php?f=13&t=6211
see pics 4th and 5th down.
If you find your transom is bad, don't be afraid to tackle the problem yourself. If you have to cut a weld, cut it as clean as possible. You can have it rewelding after the repair. Good luck!