I have a Tunze 6105 power head. Bought it used a couple years ago and have had no issues. I've had it on a pulse setting of running for 2 second then off for 2. Recently I noticed it not working. Sometimes when I grab it it will kick on and run for a few minutes then stop again. I took apart and cleaned up a bit but no real debris out anything. Still just sporadically working. Any advise on what's wrong and how I can fix it?? Thanks