My Hyper 8 used a Kyosho spur gear with a Savage X aluminum diff cup and Hyper 8 (Ofna, Hobao) internals. Shimming was required, but I think that's to be expected.
I agree on the shimming. I shimmed all my diffs (6 and 8 spiders) .
Castle Neu 1520 on 6S LiPo Powered Gmaxx (Nitro Killer)
Predator with OS .21TM
Supermaxx with Mach .26
Revo with OS .18TZ
Kyosho ST-RR Conversion
Ofna CR with Tekin ESC/Motor (2)