My imported CB550K1 came with a tank that's from either a K3/K4/F1/F2 (the one with the flap as opposed to the K1 tank which has a protruding cap). Is the K1 tank a different size from the other(s)? It seems that when I push the seat down in place it fits far more snugly over the tank than it should, so much so that it's started to rub the paint finish off the tank. If they are different sizes then I need to do a swap.