One of the gears broke on mine, so I called to order a set. They wouldn't take my money, just sent a replacement set of three. The gears arrived already on the shafts, so replacement was pretty straight forward.
It seems they had a bad bunch of gears, and would replace them under warranty depending on the serial number IIRC.
I recommend replacing all three when you get the parts and keep the original two as spares. If you only replace the broken one and another one breaks, you'll have to take the unit apart again. Not a big deal, but another thing to have to do.
chris