hi all been filling up with bio diesel recently done about 900 miles and decided i had better change the fuel filter to get rid of all the nasty bits that have come off from the inside of my tank and fuel lines. All went well until i tried to start the old girl ,I got it running but could see the air in the system through the fuel pipe,I checked in the filter box to make sure i hadnt missed a seal but there was none to seeI did a search on here and discovered there should be an o ring on the valve with the r clip I can only think the old one must of dropped of when i lifted the valve up,I searched but I think it must of dropped into another dimension because it wasnt in this one so my question is should there be one with the filter or are they bought seperately if so does anybody know the part no I asked at my local fords they said they didnt stock them thanks.