Joseph Long a.k.a. "Groovetickler" on Instagram, is the only one I’d approach stateside for any high-value / high-difficulty work. He’s shown some very impressive repair work on his Instagram history, across a HUGE range and number of cartidges. It’s worth hopping on Instagram just for that (indeed, it’s the only reason I load that app).
Overseas there are also some guys showing very impressive repair work. On Facebook, I’ve enjoyed seeing the work Sửa kim than (suakimlp.com) has done on some very exotic cartridges. And "Delta667" is a legend on the vinylengine and lencoheaven forums, though difficult to reach now being in Russia.