hang on hang on hang on.
Lots is being said here but I don't think people are really understanding how the swing arm suspension works.
Take a look at the picture below - this is the diff out of my coupe. See the 'rhino horn' pointing upward? Well that is what fixes the rear end in position in the car in a vertical sense - there is a rubber and steel mount in the trunk that the rhino horn bolts into. This does not move - so the main centre part of the rear end has a fixed position in space relative to the rest of the car - including the floor of the trunk. So, for your compensating spring to be hitting the floor, it means that the mounting through the trunk floor is incorrect. Either the mount has broken, the bolt has not been done up tightly, or it has been raised by using a spacer between the mount and the mounting position in the trunk.
Now here is a picture below of the rear end mounted in the car. See the low centre pivot point - well, its position does not move up or down once the rear end is mounted in the car (unless the mount is broken). The only thing that moves are the swing arms, in a radius as indicated by the red arrows.
So, the geometry of raising and lowering suspension is simple.
1) If the rear end is mounted as per factory, as soon as the coil springs between the car and the trailing arms are altered or the compensating spring is removed, you will get a change in camber. No question about it.
2) Changing the length of the main coil springs or compensator spring will not change the position of the rear end relative to the trunk floor. So if there is contact, it has nothing to do with springs.
3) The only way to maintain neutral camber and lower the car is to raise the position of the entire rear end relative to the car. You can do this by fitting a spacer between the rhino horn mount in the trunk and the car. However, this will reduce the clearance between the entire rear end and the car. So you could end up the compensator spring hitting the trunk floor, or the prop shaft hitting the tunnel.
Now, onto the personal attacks on wanting to lower the car. Scoot, you normally are very rational, but for some reason you are choosing to impose rather strongly your personal opinion on lowering the car on someone else. Are you going to try to convert his religion next as well? What should his favourite colour be?
The facts are that some lowering is not all bad - look at the camber used on race cars - they deliberately dial in negative camber to improve handling. However, it will impact on tyre life. If you go extreme like the airbag guys do, you run the real risk of breaking the sliding joint and then the entire rear is a throw away job. MB tell you when the diff is out of the car to basically brace it so it cannot articulate to the full extremes otherwise damage could result. Now in getting them in and out I have found this impossible to do, so I just do it gently and have had no problems in the 10 or so rear ends I have changed.
MB have many ways of subtly changing the height and camber of the rear end. There are different thickness rubber pads at the top of the main springs, and for the compensator spring, that you can buy. There are also different springs themselves, which have different coloured stripes painted on them. In the factory manual, they have what combination of rubbers and striped springs you should use for different models. I found I put a W108 rear end in my finnie, and it was way too high, even after removing the compensator spring. So I got the springs and pads out of a W110 190D and put them in - and voila, it is now level.
The only thing I will tell you to do rather than air my opinion is check the mount in the trunk. Check it is tight, check it is not misaligned. If they are ok, then pull the mount out and check if the rubber has torn or compressed heaps. New mounts should be readily available from most parts suppliers as they are a wearing item. Much cheaper than buying new springs and pads.