after ya drain the gear lub from the drive. and it's empty. i like to pressure test to see if it's sealed prior to taking it apart. then ya separate the upper from the lower to change the water pump impeller. after ya change the impeller ya put the two halves back together again. then i pressure test it again to be sure i don't have any leaks. then ya replace the gear lub by pumping it into the lower drain hole till it comes out the vent hole. prior to removing the gear lub pump, ya put the vent hole screw back in. vacuum keeps the lub in the drive while ya remove the gear lub pump and replace it with the screw. a little lub leaks out, but not enough to matter.
hth.
