Just finished installing a teflon crankscraper from http://www.crank-scrapers.com/prod01.html .
This is an excellently made product. However I should have gone with the full steel piece. Because of the back-bracing for the teflon 'shim', the bracketing was up against the 4 bolt main caps, and necessitated heavy relieving.
So the teflon should be left to 2 bolt mains, IMO. But an excellent product.