Backing Plate to Knuckle Gasket? Does it exist? Is the air gap there for cooling, or just more speed?(Joke) I know the bigger rigs have them. There was nothing there that I can recall at disassembly. Reassembled with a belltech spindle and I see an eighth inch gap (between the king pin base and the plate/cover) for crap to enter and destroy my seal. RA & local parts house say they have nothing. I found an AC 15699959, but it does not read to be anything that should go on this truck and does not look to be eighth inch thick. I'll make one if need be, but maybe you pros have ran into this.