you are spanning two model version there - W210 and W211.

There is lots of info on these, one thing to obviously consider is end of life for W210 will have all the fixes in place, early W211 will be at the beginning of the cycle.

As to 4-matic, we have that on a 2002 wagon that we bought with about 30K mi and is now close to 140K. I have needed to replace both front axles due to split boots. The axles complete can be had amazingly cheaply now (Its not worth a rebuild you just replace), and its a relatively easy repair to do yourself.

HTH
Paul