I just replaced my sending unit also. I had the same problem at first. Seems the newer ring is thinner and slightly smaller in diameter as well. still locks it in place just needs to be centered. When I first got mine in and it leaked I notice it was slitghly off center and not sealing on one side. I was able to tap it over and seal it up for now. But I did save the old ring for the same reason if it is to move for some reason. I have yet to road test mine.