I would look at the bottom to see what condition the gluvit (the coating on the bottom that helps the boat slide over the rocks) is in. While you are down there I would also look at the bottom and make sure that the bottom is still flat. Many times boats that have been used on rivers with alot of rapids will be bent, or tunneled in the middle. Check the chines for dents, and cracks in the welds. I would also check around the anchor bracket for cracks.

If the boat comes with wood oars check the tips of the blades. Many times they will put rubber tip protectors on them. This is a great place for rot to hide. I would also look at the oar locks just to make sure they still fit tightly into the polyehtelene blocks.

Hope this helps.