If the dirt has enough mineral content to be conductive, it can and will provide a path to short between two solder connections on the bottom of the board. All its got to do is provide momentary contact between two adjacent solder points and you've had a glitch of some kind. Depending on whats being shorted, you can lose contact, lose direction, lose control, lose anything the radio controls.

Most run their rcvrs in some kind of sealed radio box, thats what I do with mine. If an RC doesn't have one, I buy one made for another brand and adapt it to fit.