The set screw and thumb screw with swivel does wear out. Sanding does help, but should be replaced after time. I sell them as a set. the thumb screw with swivel is in shipping and should be here this week. The white lever also wears upon time. If if flips up for no reason, time to replace.
I posted too quick. The FedEx delivery arrived and now I have 10 in stock. The price is $7.50 per set. the link is:
Set screw and Thumb screw with swivel | Pegas scroll saw (artcraftersonline.com)