The engine is a 1985 140 and after letting boat sit for a couple of weeks ( I currently have 2 boats) the trim pump motor will develop a scale between the brushes and the copper end of the armature. Is there anyway to keep this from occurring other than running the trim pump once or so per week? Or is it time for a new pump motor. It’s a hassle to pull the pump and take it apart to sand off the the scale. Original engine still runs great.