May be just me but by grinding down the end of the water pump shaft does absolutely nothing to the force being applied to the mechanical seal. There is a machined area on the shaft itself and the impeller can only travel down the shaft so far. You could cut 3/16" off the shaft and it wouldnt do anything. Something else is wrong if everything has been replaced and its leaking. My zilla was just doing this and I made sure the mech. seal was fully seated by giving it a few more hits with a socket and hammer. My ceramic washer was gouged pretty good so i replaced it and no more leaks. The material missing from the ceramic washer could have caused an uneven amount of force to be applied to the mech seal or the seal wasnt seated properly. Just my two cents.