I asked at my local MB independent who seems very knowledgable (and is old and is german and is highly recommended on this board). He says you do not have to use the Mercedes brand. He says the important thing is that it contains anti-corrosives to protect the alluminum which is not very resistant to corrosion.
'88 560SL Pearl Black/Java 152K
'94 E320 Anthracite/Grey 89K
'94 E420 Black/Bamboo
'71 280SEL 4.5