Using WD40 would absolutely be a no no, good for cleaning something but shouldn't be actually used as a lubricant. Applying oil is really not a long term solution as oil eventually drains off where as a grease will remain in place, which I suspect was used during the initial assembly. If you haven't run the motors for a period of time (unknown how long) then I would think it appropriate to apply a small amount of lubricant prior to flying. Not known how the motors are manufactured would tell me to stick with the manufactures recommendations (they should be telling us what to use, and how often). There are brass like materials that are impregnated with oil for areas that are difficult to get to or the usage environment dictates and the bearing races could be made from something like that. BTW; obtaining an infrared signature is an excellent approach and used in many preventative maintenance programs. We had an excellent PM program at the Kennedy Space Center and would inspect electrical breaker boxes, etc. with infrared cameras to detect bad internal connections and were able to prevent some very undesirable situations (launch scrubs come to mind). We would also analyze oil samples to determine pending maintenance requirements. Having a crawler break down with a Shuttle stacked on top of it on the way to the launch pad would have been a nightmare scenario to say the least (just some of the scenarios out of thousands).