polaris 165 randomizer ball is not changing the direction of the vacuum. it get stuck in one outlet and stays there. piston is moving and spinning as it should. middle piston tube part was replaced last year and spinning piston part replaced today but ball still sticks in the first outlet it goes to. i've done all the fixes i could read about (sandinf pistons,,etc) but no luck. any ideas or am i still missing some fix??? thanks---greg