Yes, I did it.
I managed to burn a hole in my M3 shutter curtain.
After all of these years… this is a first. I had read about it but never really worried about it.
As far as I can tell, it was caused by not having the lens cap on while I was outside in intense sunlight (at the Blue Jays game). My uncapped lens likely focused the rays of light onto a small area of the shutter cloth and — voila! — a hole was created.
This is what the hole was doing to all of my film images:
(iPhone shot of a scanned image on my computer screen)
Fortunately the curtain can be easily repaired/patched.
Now I have to reconsider my w(hole) modus operandi for shooting. I have been using my lenses with protective hoods and filters but no lens caps.