are you sure it's green? the newer stock of MB anti-freeze is a straw yellow color and in an older yellowed overflow tank looks somewhat green. i found this out when my mechanic insisted that he used MB coolant and i kept thinking that he didn't. when i sucked out the coolant it was yellow. this is more pronounced specially if the coolant concentration is high. mine was at around 70% and i diluted with water which also turned it a lot paler...
1993 300e-2.8 - gone now <sigh>
"Do not adjust your mind, it's reality that's malfunctioning"