I'd contact Mom & Pops. That screw shouldn't be painted at all. It should be black chrome plate. Juice will eat paint and even powdercoat. If that screw is painted, this will not have been the first time it's happened. I can't believe any mfg would use a painted piece of hardware in this application.
You shouldn't have a big problem finding a knurled set-screw in any decent sized hardware store, but you shouldn't have to bother. They should send you a replacement. You could be seeing corrosion that ws hidden under some defective plating until it got soaked by the juice.