[Boatanchors] National NC-101X Knob Setscrew question

[Freeberg, Scott (STP)]

I replaced the RF gain pot on my NC-101X last weekend.  When I put the RF Gain knob back on, it wouldn't tighten up, so the tapped threads in the bakeline must be stripped.  I put a piece of electrical tape into the hold, and then put the setscrew in there but it still wouldn't tighten down.  

I don't have any idea on how to repair this.  Does anyone here have some experience with this sort of thing?

73, Scott WA9WFA