I have had problems for some time with crankcase fumes coming through the A/C, I don't think it is exhaust fumes, it is too strong, I thought there may be a problem with the EGR system and have been looking for oily evidence of a leak, but looking at the engine the only oily residue I can find is around the plastic oil filler, it seems a bit loose and it is not obvious how it is connected to the cam cover, I can see a plastic tab at the bottom located on a peg. I suspect that there may be a rubber O ring sealing the joint but wonder if it has worn thus allowing a leak. My wife's A4 has the same engine, the plastic oil filler is also a bit loose but there is little evidence of fumes leaking. Can someone tell me how to remove the filler so I can attempt improving the seal, thanks.