1984 300SD. I have the same vacuum problem building up in my fuel tank. I checked the fuel vent filter and it is not blocked, however I tried blowing air back through the vent line (with fuel tank cap off) and there is deffitently some sort of restriction. I tried poking a wire up the line but was not sucessful. Is there a method of clearing this line?

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My infants:
1984 W126 300SD - 118000K WVO conversion
1979 W116 300SD - 160000K Registerd Classic Vehicle