Sorry to dig up an old thread but there's enough 115 lovers out there to mention this. I just an old change on the '75 240D and you must be careful when screwing the filter housing back in place. It is very easy to not get the housing centered and seated properly. There's enough play in it to get it off center. Then as you tighten it down you are damaging the housing where it is supposed to seat to the engine.

You can use a flashlight to watch the top of the housing to make sure it is centered as you tighten it. You can also use a large screwdriver to tap it around to keep it in place.