First thing I'd try is the HTS2000 aluminum brazing rods, as I have them and they work great. Clean the hole, heat, and just partially fill the bad threads. Retap and your done. You'd have to disassemble the fork (cartridge) and most likely use a plumbers turbo torch or oxy gas torch due to the mass but the repair would be like new. JB Weld will work but has much less strength. mcmaster.com for options and any machine type tools you can't get locally.