I have used prestone on all my benz's, I have been very happy with it on the whole but I change mine every 30000 miles or 2 years religiously. When I change it I also always drain the block as well.
2005 320 CDI
2006.5 VW Jetta TDI
1991 560SEL (179000 Sold)
1972 280SEL 4.5 ('The Lead Sled' 320000 miles when sold.)
1972 220D (225000 when sold)