My Marauder Pistol (model #BP2220) does not keep pressure longer than two days.

It sounds like the O-ring (Spacer) in the gauge port assembly ( the part that connects to the Nanometer).

Here is the assembly drawing from the EVP.  We know of no wide spread issue with leaking in this area on the Marauder pistol. When the O-ring is replace the technician needs to be careful not the damage the new seal as it moves past the port hole.