The seals on the fuel filter and lines on that model car have a habit of shrinking/cracking and allowing air bubbles into the system. I know there's a very informative thread here somewhere with info on what you need to replace, o-rings and lines and such. I don't have that model car so I didn't pay that much attention. I'm sure someone can chime in that knows what you need.

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Seth

1984 300D 225K
1985 300D Donor body
1985 300D Turbo 165K. Totaled. Donor Engine. It runs!!!
1980 300SD 311K My New Baby.
1979 BMW 633csi 62K+++? Dead odo