To free the ring, invert the engine then fill the cylinder with enough methanol or acetone to get what would normally be a hydraulic lock. Move the piston through that lock and it'll force the methanol into the ring groove a bit at a time to dissolve the gummed castor. The movement of the piston will cause the ring to drag on the cylinder wall and get the methanol onto both sides of the ring. Just soaking usually won't be enough because the methanol won't be able to get past the gummy barrier. The ring is free when you look through the exhaust and can see a tiny bit of free play at the top and bottom of the ring in the groove when the piston is moved very slightly.

If the ring is gummed then the bearings will be gummed as well so they have to be freed up too. This can be done either with a bit of heat initially then flood with fuel or just flood with fuel and work them until the methanol dissolves it. When it feels free give it a full tank of fuel but running as rich as possible so there's a lot of fuel inside to flush out any stubborn undissolved bits as they come free. Personally though, with bearings I prefer to remove them to make certain they're free because it doesn't take much to make the balls sticky enough to start skidding and that's when the damage starts.