The sealing washer under the water pump impeller bolt is allowing coolant to leak between the impeller and sealing washer on 90% of the leaking water pumps on the LT 500s.  The water pump seal seldom give problems.

The water pump shaft cannot protrude above the surface of the impeller where the sealing washer seals against.  If the shaft protrudes above the surface, replace the impeller or grind about .020" off the end of the shaft.