what antifreeze for '84 500 SL ?

This is kind of divisive issue on this list...

Some people swear you need to use the "mercedes" coolant, or some orange equivalent.

Others, like me, think that is a crock, and use the good old green stuff.

The key in my opinion is to change out your coolant every couple of years at least. As long as you do this, any good quality modern auto antifreeze is fine IMO.

Marty

Use only the clear MB or the red Prestone antifreeze since it provides the required protection against corrosion of aluminum parts. Never use the green antifreeze.

Peter