Does anyone else use Penn-Plax Cascades? I have a Cascade 20 and a Cascade 80 and I've seen them both slow down. I've taken the motors off and scrubbed the impellers but they don't seem to get back to their brand-new-out-of-the-box speeds. I guess I'm asking what the lifetime of these motors is or if anyone knows some tips and tricks to get them back up to speed.