That fuel cap needs to completely seal off the fuel from external breathing or moisture ingress. Diesel fuel is highly hygroscopic. It absorbs moisture out of the air at an alarming rate if your tank has access to it due to daily cycle of high and low humidity in the air, due to adiabatic process of warm air holding more moisture, higher dew point, and cold air holding less moisture, lower dew point, and condensation inside the empty portion of this fuel tank.
Any moisture access and build up in that fuel tank is a guaranteed destroyed High Pressure Fuel Pump, and a complete replacement of the whole fuel injection system. Water does really bad things under 1600 to 2000 bar fuel pressure, including turning to steam, cavitating, rusting things, being highly corrosive when active with other elements in diesel fuel, and destroying injectors too.
RAM needs to fix that design for the diesel, and get it completely sealed off from any exposure of the fuel to daily atmospheric conditions, except when refueling.
Bosch also uses fuel as a coolant for it's High Pressure Fuel Pumps. That means when you run it low on fuel, you are also running it low on coolant. That's something you don't ever want to do on any diesel motor. Moral of the story? Always keep at least a 1/4 tank of fuel in it as coolant, running it low on fuel is a good way to destroy the whole HPFP system, by overheating it.
