In addition to what MEXICOWANDERER says, you wouldn't be buying those replacement solenoids from a non-OEM source with a lifetime guarantee would you? Can't tell you the number of times I've seen off shore white box parts come right of the box DOA. OK, it's true, I used to work in the parts dept. at a Ford dealership, but we saw that all the time. If something keeps failing prematurely, it needs a closer look and a different supplier.
Chum lee