After putting our 2 barrel 289 66 coupe back together, I have replaced the mechanical fuel pump five times now. After running the car a few hours or maybe after it sits in the garage for about 2 months, the fuel pump leaks fuel out of the vent hole in the top of the pump. I only put ethanol free premium fuel in the car. All five pumps did the same thing, only some of the pumps made a tapping noise and some did not because the amount of play in the mechanical arm inside the pump. The motor is a used rebuild engine from another 66, so I would not know if there is something wrong with the eccentric on the cam shaft. I have noticed that some Mustangs have a fuel pump that looks like it can be rebuilt. The one I have been using is the aluminum crimped (Throw away). The motor runs great, though it does need valve seals. I want to keep the mechanical pump, so I hope someone has an idea about the problem that they would like to share. Also, soon I plan to change those valve seals with good ones that can be changed in the car. Which seals would I get the best service from?