New grommet?? If it is new and fully seated onto the lip on the fuel tank, unless the filler tube isn't lined up properly, there should be no reason to leak. A little grease on the grommet sometimes helps to let things go into place better. I just did the tank on my 66 Satellite....used grease on it and made sure the tube was spotless where it goes into the grommet. There are a couple of different grommets too...You did get the right one...didn't you??