Hi Wurlitzer,
Glad I could help. That's an early-ish M3 isn't it, and I think with those, the vulcanite separates off the back door more easily, so the body vulcanite might be OK.
I think if you wanted to repair, I would remove the back door, and warm up the vulcanite in an ordinary environment so it swells a bit and regains some flexibility before re-adhering. cheers James Elwing