Years ago I used a Clearaudio Gamma, a very wide cartridge that did the same thing on my HW19III--I special-ordered a one-piece clamp from VPI- it looked like they ground the outside of the tapered perimeter of the clamp-problem solved. There is still about 1/8" of material around the perimeter that actually presses down on the record. I've used this clamp for 8-9 years now with no problems; of course I'm using a different cartridge now.
I do think the machine shop might be the answer, or you might call VPI for their recommendation
I do think the machine shop might be the answer, or you might call VPI for their recommendation