I had this problem. Darn it, now I don't remember what the problem was though. Have you read through this thread yet over at RC?
http://reefcentral.com/forums/showthread.php?t=1071516&
I think I ended up having to retire the most troublesome stream which is how I ended up with one of the spare propellers. The other spare propeller came from my other 6080 which was mounted on a wavysea and the back and forth movement caused the powercord to rub its insulation off the wire. The propellers from the two units look identical.