Yes, it's true that Mercedes does say it's safe to use Prestone antifreeze in your Mercedes. But, they state it in a subtle way.
On the Model 123 Service Manual Library Disk, they have the Owners Manual for the 1989 560SL. This manual is only an example of all their other Owners Manual,and is applicable to all models. Let me quote from page 90 of this manual and what it says about coolants. I am not making this up. Check it out.
"While there may be a number of anticorrosion antifreeze/coolants available which WILL PROVIDE the requisite(required) protection, all such products have not been tested for Mercedes-Benz vehicles. The following product, however, is recommended for use in your car: Mercedes-Benz Anticorrosion/Antifreeze Agent."
Because the Mercedes antifreeze market is relatively small, Prestone and the other major MFGs of antifreeze have not seen fit to pay Mercedes to test their products.
The last bottle of the MB antifreeze I saw was orange in color.I don't think it even said anything about the stuff called Glysantin G-05. Zerex is orange. Both are made by Valvoline Oil, a division of Marathon-Ashland.
I just checked the owners manual on my 1982 300D-turbo and 1983 300SD. Both have the same quote as above about the coolant. As for my 1977 300D, the manual only states, and again I quote; "Any Mercedes-Benz service station will readily advise you on recommended antifreeze brands."
When I bought my first MB (1967 200D), the dealer said I could use any brand of antifreeze I wanted to use. I chose Prestone and I have used it for 34 years in all the MBs I have owned. I have never had any problems with it...
Bill Lewallen; Lexington,Ky.
Home of Valvoline Oil-The maker of MB antifreeze,but It's not made in Lexington...