I researched rebuilding/aftermarket impellers before I ordered my kit, came across a couple of sources that should be able to help with parts
http://www.928motorsports.com/parts/...ebuild_kit.php
http://www.superchargerrebuild.com/vortech/
Some even sell upgraded bearings for higher RPM usage. Not sure if the stock vortech impeller is good for faster speeds or if it was limited by the bearings vortech uses.. but its worth a shot if you want to try a very small pulley that would normally put the blower past the recommended max RPM.
They also include a better set of seals (or so they claim)
I know mine seeps oil VERY slowly, not enough to even register as a loss on the dipstick but just enough to make a damp stain on the supercharger. Maybe a few drops every oil change.
Check here for upgraded bearing rebuild kits
http://www.928motorsports.com/parts/...ebuild_kit.php
Also, what is the reason for rebuild? Bearings start getting noisy?