What is the difference in the O ring colors as they come from Mercedes? For my recent delivery valve/fuel line O ring replacement job, I received mostly black O rings from MBUSA. I understand them to be the nitrile/buna rubber composition. However, there were a couple of O rings that were green in color. Two were for the fuel pump and the other was for the banjo bolt on the fuel line that bolts into the back of the injection pump using the two copper washers. The size isn't the difference because they were the same size as some of the black ones. I did replace all of the Mercedes supplied black O rings with viton though.

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Len
'59 220S Cabriolet-SOLD and living happily in Malta
'83 240D 351,500 miles original owner-SOLD
'88 560SL 41,000 miles - totaled and parted out
https://sites.google.com/site/mercedesstuff/home
'99 E300 turbo 227,500 miles
'03 SLK320 40,000 miles - gave to my daughter
'14 Smart electric coupe 28,500 miles
'14 Smart electric cabriolet 28,500 miles
'15 Smart electric coupe 28,000 miles