You can always try locktite.
Make sure you tighten down the pinion on the flat part of the motor shaft and you should be fine.
Xray T2 US '007, JR Z590 servo, KO PROPO EX-10 Helios, Novak GTB, Novak 13.5, EP4600?, Orion Advantage.
Sportworks Recoil - MMR Spec, GTX
Additional Feedback: http://rctech.net/forum/showthread.php?t=145047