The bigger issue would be to look into what caused the coolant tank to become low. There is really no reason for it to leak out. Make you have a hose with a pinhole in it, or the hose clamps need tightening. For now Id find out why, then I'd think about flushing the cooling system while your at it with MB coolant. The thing is Mercedes coolant is made for mercedes and it has a low acidity. Acidic coolant ruins engines.
No Benzes in the stable at the moment, but itching for one again.
Former Mercedes in the Stable:
1983 300CD Turbo diesel 515k mi sold
1984 300CD Turbo Diesel 150 k mi sold
1982 300D Turbo Diesel 225 sold
1987 300D Turbo Diesel 255k mi sold
1988 300 CE AMG Hammer 15k mi sold
1986 300E Amg Hammer 88k mi sold
1992 500E 156k mi sold