Hey all, my wife's been complaining about the mirrors on our '85 245 constantly falling out of adjustment, so I've been wondering if the fixed housing mirrors from a later car will bolt up to the '85's doors?
Which of the two adjustments are loose? If the mirror tends to fold in towards the car, you might be able to fix it by tightening the screw on the underside of the mirror. If it's the other one (towards the road or towards the sky), I'm not sure. I put an old style mirror on my '87 244 becase I liked the way it looked, and I've noticed it will turn downward slightly after some high speed highway driving, but it doesn't bother me yet.
As for whether the new mirrors will fit the old 240s, I can't say for sure, but the old mirrors fit the newer 240s just fine. The holes matched up and the trim fit perfectly on the inside and outside. I bought my mirror for $12 from a junkyard (I also removed the passengers side mirror and used trim from an old DL that didn't come with one).
I've been told that an extra hole needs to be drilled to fit the newer style mirrors on an older 240. On the old style doors, there's a large hole in the center of the triangular mounting surface where the inside portion of the mirror is screwed to the outside portion, holding it to the door. The newer style mirror is held on by two screws, one above and one below the adjuster knob. You'll have to drill at least one hole through the metal of the door.