Your 1976 240D should have the canister filter that is mounted under the car, and it should have a plastic filter screen too. On the canister it shows the part # for both the screen and the filter.

My W115 300D is missing the plastic filter screen, but i have been told its OK to run it with out that screen installed.

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1985 300TD Turbo Euro-wagon
1979 280CE 225,200 miles
1985 300D Turbo 264,000 miles
1976 240D 190,000 miles
1979 300TD 220,000

GONE but not forgotten
1976 300D 195,300 miles
1983 300D Turbo 175,000 miles

http://i42.photobucket.com/albums/e3...e485-1-2-1.jpg