Iron block & Aluminum head
You know MB isnt the only manufacturer to have problems mating a cast iron block to an aluminum head.
My first car which I saved the proceeds from many summers of what seems like slave labor now was a 1988 Olds Cutlass Calais coupe. It had the at the time somewhat modern 16V dohc Quad 4 2.4l 4 cyl in it. And the infamous cast iron block and aluminum head.
I got it in 92 with 56k miles. Well needless to say, at 58k a couple months later, it blew a lower radiator hose, and overheated pretty bad.
Well I finally had it towed home, went to the parts store got the hose bla bla bla... started it, and what do you know, plumes of white smoke. Head gasket had failed.
So, I called a bunch of Olds dealers, and I found out that it had been a chronic problem with that motor, and there was a goodwill warranty till 6 years 60k miles, and they took care of the head gasket. Talk about cutting it down to the wire.
Anyway, from what I was told back then, and what I have discovered, basically any significant period of overheating, or consistently running the motor hot will cause the head gasket to fail. This has to do with the different expansion properties of the two metals. As they get hot (beyond normal operating temps), they expand differently, and the head essentialy begins to warp, and break the seal between the head and the block. Hence the head gasket issue. In an extreme overheat, It will warp the head, at lower temperatures, it will cause premature failure of the gasket.
Best wishes and take care,