I have a pre-filter on my '74, I would think you'd need one to protect the lift pump, a small clear plastic in-line filter right before the lift pump. You'll need a short piece of fuel line and two more hose clamps to install a filter there if you don't already have one.

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1985 300TD-euro 352,000 mi
1974 240D (1?)52,000 mi - has a new home now