Thanks, you're right. I see now that Terry's would have worked, but I did not take Terry up on his generous offer. My loss.
Instead, purchased a fin from a local salvage place -- Faeth of Sacramento -- for surprisingly cheap at $300. It should arrive Tuesday.
I did not think I would be replacing the tail fin of my airplane, but I guess that's what paint stripping and inspecting are all about...finding problems like this. My old fin was compromised near the bottom rudder hinge. It would have driven me crazy knowing this piece was rotting away. So, I'm fixing it.
