You're ringing some bells here with this LMS hypothesis. I did jockey a cold car into the repair-bay side. It does crank like crazy. I do smell gas when I manually crank it.

I wonder if hypothetically the valves are sticking, or if the rings are rinsed clean by a rich cold mixture. I might drop some Marvel Mystery Oil into a piston, to test if I can get compression back. Honestly, it cranks like the valves are open. If I remove the oil filler cap, I expect I might notice blowby from the rings.

Fascinating! My despair is changing into hope. Thanks for throwing me a rope. I will post the outcome, tomorrow.