I just finished installing my Castle 2200Kv motor on my ST RR and noticed that the motor shaft have about a 2-3mm fore/aft play. I didn't notice this much play on my TeknoRC Neu and Medusa motors.
Here's a vid:
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)