Flippers, the comparison you made is apples and oranges, the 6205 is a DC pump and has a transformer, it is also repairable and individual components can be replaced.
You first have to understand how a GFCI works, many people have the false assumption it actually detects stray voltage or shorts to ground, it does not. It trips when more current enters on the hot lead than exits on the neutral. Any device which has or acts like a capacitor and stores current will trip a GFCI as part of its normal operation. This can include motors, ballasts, and transformers.
In this case I suspect one of two issues, the motor, while lacking a capacitor, will act like a capacitor if the drive unit is jammed and I suspect this is the issue because you mentioned cleaning resolved it. It builds a charge as it tries to spin the propeller, my guess is the shaft is coated with calcium deposits and the magnet with propeller cannot spin easily on the shaft.
The other possibility is that the power supply is failing and it is also possible that GFCI is faulty. Modern GFCI's are so sensitive that there is often no safety issue, they just are overly sensitive and cannot run with any sort of capacitative load. My house was recently remodeled and the GFCI's and AFCI's infuriate me, my only saving grace is that the garage was left alone but I cannot run my welder on any of my outdoor outlets and I have a flourescent bathroom fixture that will randomly trip the GFCI though there is no apparent issue with it. The price of safety is apparently a huge pain in the butt.
