To do the job properly you need to take the motor apart to get to the sensor board PCB. This needs to be lazy goo'd or plastidip'd, myself I use plastidip
Something that is cold and wet, then gets really hot will produce condensation both externally and internally. This is why you see cars run for 5 minutes in the first heat then stop working. Then the same gear is fine a week later after its dried out.
If you want to see more about this have a look at the round 2, Cotswolds video on
http://www.rcracing.tv/ its at the bottom of the page.