I used ATF & thinners for three weeks on a Villiers Midget that was seized up with no success so the threw the whole thing into a bucket of diesel for a further three and a bit weeks. I was suprised to find that it was free enough to turn and get the piston out at the end of this soaking. Don't know if it was one or the other or a combination of both that did the trick but that motor is now running on my Ransomes Minor Mk 7 so be prepared to try everything if one doesn't work.
