The saga continues. I pulled the boat apart - came easily. There was a powdery residue in the beam recesses that I thought might have once been a construction glue and used during an assembly at some time. It all cleaned out easily.
Some corrosion, especially where the dolphin striker was fixed. After tensioning the striker (easy) I have thoroughly cleaned out the corrosion pits and let in a bit of epoxy, followed by some chopped carbon fiber. I'll probably put some more strips of carbon over the repairs and cross fingers that all that will return my beams to a serviceable condition.
My centre boards are back in, but pretty wobbly when down. I was thinking of packing the inside of the case, near the bottom, with some Teflon strips. Any other ideas appreciated.