Mechanical fuel pumps keep quickly leaking fuel 73 cj5 304

I inherited a 1973 CJ5 with a 304 about a year ago. Shortly after I got it the fuel pump started leaking fuel from the horizontal mid body seal. I replaced it, then began having other fuel issues, old tank, sediment, leaks in the line. I took it to an experienced off road shop, and had them replace the fuel system; tank, lines, filters, pump. The shop said they needed to put a pressure regulator between the fuel pump and carb, because there was fuel coming out of the carb after they replaced the system before returning it to me. It ran fine for about 2 hours of operating after getting it back from the shop and then the fuel pump began leaking from the mid body seal. I replaced it myself, and within 10 minutes of running, it too began leaking fuel from the mid body. Any idea what would be making the mechanical fuel pump keep blowing up so quickly? It does not have a return line, and I wonder with a mechanical pump what keeps the pressure from building inside of them if they keep pumping and the fuel is not needed at the carb?