Just before I start, erubin, your '72 450SL has plenty of aluminium (for example, the cylinder heads, the water pump, the themostat housing and hose connections to name a few). That shows how much the person advising you knows!
As for coolant, my '73 350SLC that I have owned for the past 20 years has always had a name brand coolant (eg. Castrol) but never MB coolant. To date, I have had no problems I would consider coolant related. On the two occasions when I have had a water pump leak, it has been due to the failure of the rubber behind the seal rather than the the carbon/ceramic seal itself. As for aluminium components in contact with coolant, I can see no more corrosion on them than 20 years ago when I purchased the car. All cooling system components apart from the water pump are still original. Only recently did the radiator require a repair for a minor leak.
If I then take our '90 300TE. A few years back I had to replace the head gasket due to the familiar oil leak at the rear corner of the head and the eventual oil in the coolant. Inspection of the head gasket revealed severe corrosion around all the water passages. Fortunately the corrosion was restricted to the gasket and not the head or block. This all occured not long after our purchasing the car, a car with MB dealer service history and presumably MB coolant.
Yes I do now use MB coolant, but probably more for the fact it is not much more expensive than a good name brand from elsewhere and I figure that it hopefully is no worse than the other brands. I also change it annually (rather than 3 yearly as recommended in the service manual) following the experience with the 300TE.
Also, when talking MB coolant are we all talking about the same thing? In Australia it has always been dark blue. I believe in the US yours is orange. Can they both be equivalent MB coolant?
107.023: 350SLC, 3-speed auto, icon gold, parchment MBtex (sold 2012 after 29 years ownership).
107.026: 500SLC, 4-speed auto, thistle green, green velour.
124.090: 300TE, 4-speed auto, arctic white, cream-beige MBtex.
201.028: 190E 2.3 Sportline, 5-speed manual, arctic white, blue leather.
201.028: 190E 2.3, 4-speed auto, blue-black, grey MBtex.
201.034: 190E 2.3-16, 5-speed manual, blue-black, black leather.