A fuel pump for an internal combustion engine comprising a barrel having a longitudinal axis that spans between a proximal end and a distal end and a central bore therein. A plunger is disposed at least partially in the central bore and is configured to move along the longitudinal axis. An annular seal assembly is arranged around the circumference of the plunger wherein the annular seal assembly includes a seal retainer housing and a first seal and the seal retainer housing also retains the proximal end of the barrel thereon to form a second seal wherein the first and the second seals reduce the fuel to oil transfer rate and the oil to fuel transfer rate. The plunger and barrel are configured to be removed from and re-assembled with the annular seal assembly to enable service of these parts and the fuel pump.