I know this thread is a little old, but I want to describe my experience with the Mamiya-Sekor Press 65mm f6.3 lens. Late in 2021, ealy 2022 I bought a gorgeous 65mm F6.3 from Japan on ebay. When it arrived, the focus was a little stiff, but rapidly became stiffer until it reached the point of "if I could get it back to focus at infinity, I am going to only use it for landscapes anyway". My repair guy, who was swamped as usual, recommended I put a TINY drop of Marvel Mystery Oil on the helical focusing threads that are visible from the back of the lens with the point of a toothpick, and try to work it in by moving the focus. One drop did not do the job, but one drop each day over the course of a week DID! If you don't have that brand oil, I would not recommend the usual form of penetrating oil. Marvel oil is a little thicker than that and takes its time to move around. Hopefully you would have something similar after a search The focus remained smooth for the next year or so that I used that lens until I sold it and my Mamiya press outfit.