A 3.07 (which I have in stock) is an excellent diff swap for a 240D. I have personally swapped this into a couple of customer 240D's. I believe Uncle Kent Bergsma has a video of him doing this diff swap on youtube and you can actually see the acceleration.

It will be slightly slower on the takeoff, but the 240D is already one of the slowest vehicles on the road, so a second or two off acceleration is not too noticeable.

The benefit of this swap is that freeway/highway cruising RPMS will be lower and the car will be considerably quieter/tolerable at 70 mph than with the 3.69 differential

I agree on the ratio problem. My 1984 300D spins ~3000 rpm at 65 mph. When I return to driving it after my other vehicles, I often look to insure I have it in "D" because it seems like there should be another shift. My 1985 CA supposedly has a slightly taller rear, but it still seems to spin too fast on the highway, maybe 2900 rpm. My 1996 Plymouth Voyager only has 3 gears but the engine feels comfortable at 70 mph, so probably spinning 2500 rpm (no tach). Seems like the M-B designers could have been smarter in spreading out the 4 gears they had to work with. Heck, the early 1960's Corvette only had 2 gears.

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1984 & 1985 CA 300D's
1964 & 65 Mopar's - Valiant, Dart, Newport
1996 & 2002 Chrysler minivans

not slightly slower. Way slower off the line! Been there done that. 3.69 or 3.46 are the ticket.