I did a flush on my '87 420 last year and I recall that the procedure needed about 1.5 kg i.e. 3 containers at 500 gr. at $16 from MB. I believe the container mentions the amount of water or the CD. You have to let it run for 15 minutes at 2500-3000 rpms. Then drain and flush with fresh water and eventually fill with MB coolant (at least 40% solution for anticorrosion protection).
During the flush you want the heating on so the stuff goes also through the heater.