I have now emptied and dropped the tank twice in as many days. the first time I did it I pushed the gasket onto the filler pipe before inserting it into the tank as other people have stated they did. There is only one problem with doing it this way... When you put the filler neck into rubber gasket before sliding the filler pipe into the tank, it expands the rubber gasket, and prevents it from seating into the tank. Mine slid right up the filler pipe and never seated in the tank. When I filled it up after the first time the leak was even worse than it was originally.
The far easier way to replace that gasket is to snap it into the tank. I applied a very very thin film of grease (NOT silicone grease either) The Ford TSB says to use petroleum jelly to the filler neck. Then I had someone else watch the filler pipe and make sure I had it centered in the opening as I pushed the gas tank back into position. The only way you are going to push the gasket into the tank is if you do not pay attention to the filler neck as you push the tank back up into position. Once the filler pipe is started into the gasket It is not possible to push the gasket into the tank as the filler pipe expands it.
Its not a very difficult job to do if your tank is almost empty. I had to pump 6 gallons of gas out the first time and 10 out the second time. The most important part is to make sure the filler neck is centered in the gasket as you push the tank back into place.
