Not trying to send you someplace else, but I posted an update to this thread at anything-sailing.com and have received some good replies back. (Didn't remember that this is where I posted the original question until someone over there reminded me.)
I removed the rub rail and found a mess of old holes. So now this is a pre-launch priority fix, along with fixing the keel spalding, seacock fixes and bottom painting.
Latest picture is here:
other thread is here: Holes under aft rub rail
Great minds discuss ideas;
Average minds discuss events;
Small minds discuss people.
The best minds discuss sailing, anchors, batteries, rode length, fridge-or-not, freezer-or-not, and guns-on-board. I don't know why. It's a mystery!