For the W124 chassis, I believe the 4-matic is available during 1990 - 1993. Generally, the system is considered as overly complex therefore not reliable. Transfer case leak (internal and external) is what I heard as the main cause and fix is not cheap.
I also heard that the newer systems are much simpler so more reliable.
To me, I still prefer simple systems because they are good enough if I use good tires, good caution, and good driving skills. As MB says in the sales brochures (I paraphrase): no system, no matter how advanced, can overcome the laws of physics.
These 4-matics, traction control, etc., are all problem areas. I have read enough from this forum that when one of these electronic system malfunctions, you "limp home" and then pay top $ for costly repairs.
The longer I have the 1987 300TD, the more I like it. I do like my 1997 E320 but it is still fairly new so everything is still working. I wonder if a OM61X powered car will make me even happier.