Tank Filler Pipe And Cap problems of the 2001 Mazda Tribute

Wife stopped at gas station to fill up. Car would not start after fillup. Had car towed home. Determined it was a bad fuel pump. Replaced fuel pump. Should have been a simple repair, but it was anything but simple. Completed fuel pump replacement, with no further problems. About two weeks after replacing the fuel pump, my wife and I started smelling fuel outside of the car. I removed the cover over the fuel pump, but could not find a leak. I looked under the car, and observed a gas spot on the ground just forward of the fuel tank, but still can't find the leak. Car runs fine, but the gas mileage has dropped to about 10 to15 mpg, from 20 to 25mpg. There are no caution/warning lights on the dash. Had an ase certified mechanic friend of mine look at it. He could not find the leak. Does not leak all the time, and when it does, it appears to be only a few drops. Mechanic recommended a fuel filter change, and perhaps a dye test to make the leak easier to see. We have had this car since Feb. 2013, and the fuel pump is the only major problem we have had, not counting the four new 16 inch tires we had to replace at the time of sale. I still love this car, v6, awd, sunroof, leather seats, ice cold air, cruise, tilt, power windows, locks, seat, ect. Ect. Have had people swore it was a new car. They could not believe it is 12 years old. I take real good care of my cars. Wife swares I love it more than her. I have had my wife for over 20 years, and don't plan to trade her, or the car, in anytime soon.