Gary and others, if you get a chance please could you message me with the exact nature of your motor problems? It would be useful to know if the problem is consistently isolated to the motor rather than the gearbox, one way of checking this is seeing if the motor shaft (when removed from the gearbox) is any stiffer than you would normally expect and/or if the no-load current is much greater than the rated value (1.4A for the 12V at 12V, 0.85V for the 18V at 18V and 0.7A for the 24V at 24v). Also if there are any other signs of damage or visible stress points.
It is possible that lack of support for the rear of the motor body is contributing to problems in the shock-environment of combat, though I would want to be sure of this before investing in a remedy.