Some B&M's were stripped. They use Teflex rather than teflon. Wears much better. A lot of 6-71 & 8-17 use teflex also on the non competition blowers. Littlefield etc. The main reason for it's use was purely for marketing purposes. The average users were wanting their blowers stripped. You will notice they do not wear out like it would if it was Teflon.
As recommended, let the boost guage and visual inspection determine when to have it replaced.