Warning: soaked a stuck focus ring in lighter fluid and it ate the grease right out
Had a Canon FD 50mm with a focus ring so stiff you could barely turn it, so I dripped lighter fluid into the gap like some old forum post said to do. It worked great for about a day, then the ring went loose and gritty because the fluid washed the factory grease out of the helicoid. Ended up pulling the whole lens apart, cleaning it, and relubing with a proper lithium grease, which took me 3 hours on a lens that should have been a 20 minute job. If a ring is stiff, just take it apart and do it right the first time. Anyone got a favorite grease that holds up longer than the white lithium stuff?