I have a Challenger pump.
Pool store "A" tells me that the biggest killer of pump motors is rear seal failure. They point out that the place where it seats has some circular grooves in it. I can feel the grooves, but can't see them. They tell me that it came from the factory smooth, and they suggest replacing the entire rear plate to the pump body.
I don't show interest in spending $ on it, so he proceeds to assemble it. He takes a glob of silicone grease and put it between the rubber of the rear seal and the surface that he said was worn, then presses it in.
Pool store "B" doesn't use any silicone grease. They say that pushing it in place is sufficient and the rear seal is a spring design, and the impeller + seal assembly keeps it pressed in place. They say grease would actually lubricate and help the seal to spin, more so than it would offer a more water-tight seal.
I'm personally thinking I should silicone calk the rear seal in place if this is really a significant concern.