Water pump shaft - the Rev3's have a nylon drive gear with a metal shaft, the two are held together by a pin that slides through a hole in the base of the shaft and locates in a recess in the back of the drive gear. The shaft comes through the inner case, impeller goes on, then circlip goes on to hold it all in place. So sounds likely that the circlip has come off for some reason, this would allow the shaft to go back through the inner case slightly, pin to drop out, and probably munch the nylon drive gear - hence it doesn't spin a full 360° any more.
So, I would suspect seal was actually OK, but movement of the shaft has let the oil in, as it's going to be apart, replace the seal as it will need doing sooner or later anyway.
You'll need: Nylon drive gear, new pin, seals, circlip, 'O' rings and gaskets for inner case & water pump housing.
Suspect cases will have lots of little bits of white nylon from the drive gear in there so try and get all that out while it's apart.
Water Pump Bits: http://www.haventria...183_158_191_873
I'd say you'll want 20,22,25,27,36 as minimum, check the impellor, maybe consider doing bearings also for the price of them - 23 & 34.
Would think you'll want 11 &18 off this diagram also: http://www.haventria...183_158_191_852