I replaced my pulley seal but it appears to still leak. Is there a sleeve available for the impeller hub or is the hub a common item which sometimes needs replacement?

I've seen a couple of grooved hubs that were beyond use, but it's not a common problem. You have adequate breathing for the crankcase? Did you change the o-ring, too? The Cap'n

The last post was right, There is an O ring behind the hub. You will probably have to use a puller the get the center hub off the crank. This O ring is often left off or not changed during a rebuild.