I recently managed to un-stick a Singer 99. Both the needle bar and the presser foot bar were stuck. I have had the machine maybe a year, I don't remember. I had worked on it, oiled it up and decided to let it have some time for the oil to work. I decided if I couldn't get it unstuck it would be a parts machine. So I tackled it again. Put tri flow, oil and finally some break free. Still stuck. Finally got the presser foot bar moving by tapping on it. The needle bar was about half way up. Tapped, tapped. Left overnight. Tapped tapped, left over night. Tapped some more, going up, tapped going down. I had made a mark on the bar to see if it was moving. Hey the mark had move a 32 of an inch. Hey a few more taps and it moved 16th. More tapping and finally tapped it clear down, then back up, with taps. At last it was free- applied more oil wiping up the excess and spinning the movement. Oil coming out was orange, yes it was rusty.
How is it now, it is one of the smoothest movements of a 99 I have. Sweet little machine. Next challenge is the motor, bad wires and doesn't move freely. I may just replace the motor. Would put a handcrank on it but it has a solid wheel and the spoke wheel is too thick.
Sorry if I have rambled on a bit, good luck on the sticky problem!
Ethel