Here's a simple fix when your pump still drips and all parts are in good shape. I'm sure all who own a 500 motor have or will run across a leaking waterpump at one time or another. I've fought leaking waterpumps for years even when all the parts are new (impellar shaft, impellar, sealing washers, waterpump seals). The impellar always seems to loosen up on the shaft even when locktite has been used. So I've figured out a simple way to fix this problem. Use a sealing washer off of a brake line banjo bolt, install the impellar on the shaft, use the banjo washer next, fits perfectly over the shaft, put a little silicone on and then install the other wahers and bolt and torque down. This seats the impellar all the way against the end of the flats on the shaft and locks the impellar in place. No more drips!!!!!