Glad you found the culprit. Lens inverts the image. Pinhole on top. Leak on top of film which translates to the bottom of the image.
In the 70's I had an M2 and an M3, usually with the 90 or 35 Sumicron attached.
One day I saw something like this, and I realized that I had carried the 90 camera around in my car for a couple of days without the lens cap.
Apparently, it sat for a long enough period, pointed up (following me here?) toward the sun.
Remember the childhood trick with the paper and the magnifying glass, and the sun? You bet, burned a hole (nice clean round one) in my curtain, based on how it was focused, etc. One nice thing about SLR's, there's a mirror to prevent this.
I never went without a lens cap again.
Might this have happened to you?
This may have happened to me. Though I am aware of that being an issue so I try not to ever face it into the sun. Still doesn't make it impossible though. The obvious solution would be for me to just get a damn lenscap!
Originally Posted by George Collier
It needs to be stationary for a few seconds leaving it sat on outside pub or coffee shop table bad. Even neck strap risky.
Exaktas tend to get sunburn on second blind and go brittle cause they dont have an instant return mirror.
Shutter rebuild expensive. Cap cheap.
I bought some liquid electrical tape and patched the holes, I discovered more than 1! I also bought a lens cap. Next time it needs CLA I'll have the shutter replaced, but it works great for now.