When the selector is pushed in, the shaft it's attached to will actually protrude from the back of the machine. Is it currently tight against the body, or is it sticking out the back at all?
I'm going to make a weird suggestion. Use the flat of your hand, and give that top stitch selector a bit of a "bump". About as hard as you'd have to hit a bottle of triflow to knock it off the table, not too hard, just a slight attitude adjustment. I did this to the estate sale machine that I had, we're pretty sure that that machine wasn't used for 20 years or more and one slap and it freed up immediately.
Hopefully your skate shop carries the TriFlow. All the shops here carry the FinishLine products. I lucked out and found it at 2 bicycle shops. Possibly the only 2 in Edmonton.