1997 ford f 150 4.2 liter engine the transmission cooler lines were leaking.?

I HAD A MECHANIC REPLACE TWO.WHEN I TOOK THE TRUCK HOME I NOTICED THAT THE TRANSMISSION FLUID WAS LEAKING FROM SOME WERE ABOVE AND LEAKING DOWN THE MIDDLE OF THE PLASTIC THAT GOES AROUND THE FAN.ONLY LEAKS WHEN TRUCK IS RUNNING. THE LINES THAT THE MECHANIC REPLACED SEEM TO BE FINE.ANY FORD MECHANICS NO THE ANSWER.THANKS DAN