I have a similar problem that has to do with the feed dogs, but that I was able to trace back to the reverse button. I'm trying to resurrect an old machine and the reverse button was completely gummed up. Yours looks much newer and nicer than mine, but it has the same reverse button, so I'm guessing the internals may be similar. I took off the end and the top and shot all the joints and levers liberally with PB Blaster as recommended above and the button eventually freed up. There are a lot of levers, cams, gears and springs that come into play to make it run in reverse. From what little I know, if they get balky and gummed up, the old oil and grease need to be dissolved to get things back on track. I posted as Universal Model 5510, if you're interested.
Last edited by Noel; 03-23-2013 at 11:02 AM.