Preparing for a retrofit that has DC brushed servo axis drives. Resistance for motor chassis ground to motor power leads for one motor is 4.0 megohms, 0.63 M for the second and infinite for 3rd axis. All axes were tested for function and working fine prior to the test, but I'm pretty sure these readings should all be infinite. Is it possible there is some carbon dust inside from wear to brushes causing this? is it an issue that needs to be dealt with or can I ignore it? It is a used machine with some mileage on it but in good shape. I've never taken apart a servo motor; one of the motors with the issue also has a brake. I'm not too keen on taking the motor apart as I've heard rumors of that being a one way ticket to failure but I don't know if that's true or based on someone who is not very careful . I do not want to screw anything up, would the best course of action be to remove the brushes and try to vacuum out any carbon dust then use a blowgun with all the brushes out, or what? These will be used with an expensive 3 axis integrated servo drive/controller that I need to protect over all....