Mine had the same problem. The O rings are in that valve, and it comes apart easy (for me). Finding the right O-rings is essential. I could not. I saw a Cummins website forum (not here) where some guy said he talked to a guy at NAPA and was able to order the right sized O-rings made from a special type of rubber (I forget) that is fuel resistant
. I tried, but the NAPA where I was could not figure it out. I was on the road, so no time for the long search...
I have a box of universal "standard" O-rings, none fit; maybe if you can get the "metric" box, one in it would fit. It needs to be the right thickness, and have the right inner and outer diameter.
I ordered a whole new valve from these guys:
They took very good care of me. I ordered one based on a 1999 Dodge Ram pickup, since my bus is a 1999. My motor is found in 2000-2002 Rams, though, so I had to return it, and they sent me the correct one based on my motor's serial number. I would suggest you email or call them with your motor's serial number (not your VIN number!) and ask them to assist you in your selection, if you can't find new O rings. Maybe even send them a pic.
I found the steel lines leading into the fuel filter canister were not too tight, but if they are on yours, get yourself a flare nut wrench
to loosten them: don't strip your fuel line nuts. I like to sneek stuff on/off without removing too much other stuff, but I did have to remove the whole canister to get the valve off the side.
The valve drains the canister when changing the fuel filter, so no unfiltered diesel or gunk gets into the injector pump.