Try your MB dealer, they have to dispose of the stuff they change. They have taken mine before - no charge. They always ask to be sure there is no antifreeze in the oil, as it gets sold to a recycler and its worthless if there is antifreeze in it. So unless you're mixing cocktails, they should take it. Also, just about any autoparts store or gas station will take my old oil in Toronto.
1995 E420 - retired
1986 420SEL - retired