I have used the same bottle of singer machine oil for the last 10+ years and have used oil and lub from my Singer 221 that was 80 yrs old and they were still good. I would say afterward, they sing like a singer.
I have also used the oil with no problem on older Kenmore's, Juki's, and Brother's with out a problem.
I hope this helps a bit. A lot of good information has come your way from so many others. If the oiling and simple maintenance doesn't work it may be time to take it in for a tuneup and see if something else is not right.