I think I got mine at Pep Boys for about $11 or so; it was a couple years ago so I'm not positive. With that said, I'm about due and will be flushing the E320 again soon.

2 gals of Zerex might cost $25, and 2 gals of generic green coolant might cost $8. You're already saving on the labor by doing it yourself; is it really worth saving another $17 by using the "wrong" stuff?

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08 W251 R350
97 W210 E320
91 W124 300E
86 W126 560SEL
85 W126 380SE Silver
85 W126 380SE Cranberry
79 W123 250
78 W123 280E
75 W114 280