Mitch I would give a good hard look at your transom because if its not sound any work that you do will be a waist of time. When the plywood starts to rot out the torsional forces of the engine is taken up by just the glass that was never meant to carry these loads alone. The stress will show up at the weakest point in your case the rivets holding your cap/liner to the hull. It would be neat to pull a string from between your damage at the stringer and the stress point on your liner (Third picture) and see if it points close to the center of where you unzipped your gunnel. On my Seavette we found damage that pointed to close to the same area only on the starboard side In my case the top and hull were mechanically fasten by though bolting not rivets so the fiberglass took the hit.
