2012 M6040. Im having issues with it stalling and it seems to be getting air in the injector. It all started when the 1/4" return fuel line popped off going back into the fuel tank. I put it back on. I didnt run it out of fuel or nothing. It would stall and starve for fuel at 2000 RPM and eventually die. I drained the fuel separator and have changed the fuel filter twice. I sucked the fuel out and then changed the fuel filter the 2nd time. I notice the fuel in the water separator cup gets about half way down at times. I have had to bleed the injector to get it back going. I did confirm that my O-ring was on my separator. Got any suggestions?