A/C refrigerant leaks at fill port

Hi,

My stepson replaced the A/C Refrigerant Liquid Hose in his truck listed above as he stated it was bad. He charged the system via connecting to the port on the new hose (metal line). The A/C worked for a short time then he found the refrigerant leaked at the filling port. He replaced the hose (metal line) with a new Motorcraft part and the same failure happened again. Is he doing something wrong or is this a common problem? What to do?

My stepson has done extensive auto repairs.

Thanks,
Tom