Though MB says itself relentless pursues perfection, I think the current 4-Matic is technically a big compromise MB made.
The old 4-matic has 3 differentials, two of them (Center and rear) can be locked automatically, Torque distribution between front and rear can varies from 65/35 to 100/0, in normal driving, transfer 100% torque to rear wheel to save power train loss, even nowadays, most of real offroad vehicles don't have such advanced 4 wheel drive, it can pull out itself even when only one rear wheel has traction, it can only be stuck when both rear wheels and one/both front wheels lose traction, and most important, it uses locking differentials which make it tough and can be use constantly in harsh environment.
I feel sad that MB failed to improve the reliability of this advanced complex system, and just walked around with some inferior solution. I don't know what kind of center differential current 4-matic uses now, but since it distributes torque 35/65 permanently, I would think it just a cheap viscous clutch differential, and uses brake to transfer torque to the other wheel, it may be reliable, but is far less superior than the old 4-matic, good thing to Mercedes is they could significantly cut the cost.
99 BMW 540i 6-speed 110K Km
03 SAAB 9-5 wagon 80K Km
92 400E (Sold) 245K km
Still missing the days with the Benz, it kept me busy.