My Performer RPM manifold instructions as are most aftermarket manifold manufacturers were very specific about NOT using the end seals, they like to blow out under high load when crankcase pressure can rise. The Right Stuff only comes in two kinds, a regular kind (similar to Ultra Black) and one for "Imports" (more like Ultra Grey.) Both work just awesome, but any other good RTV will also suffice. Usually need a good 1/2" bead to do the job, don't forget to overlap on the actual intake gaskets or you'll have leaks in the corners.