mine did the same as well, had to add shims but the spur is thinner than the pinion so i just had it set so the spur was always 100% on the pinion when it moved, also had more even wear on the pinion this way.
Losi Muggy
medusa 36-80-2000kv
6s turnigy 30c
MMMV3
46ts/ 14-16p
spektrum radio