We had this discussioin on that other mercedes mailing list a few years ago. To settle the question of topsider vs. drain plug, George Murphy actually performed some experiments to gather empirical data. For those of you not familiar with him, George is one of two or three main technical advisors to the Mercedes Benz Club of America. Apart from the politics of that organization, he really knows these cars.
What George did was mount the oil pan - I believe it was from a 123 300D - and fill it with water. He then drained it using the plug, and measured the remaining water. He then repeated, using a topsider down the dipstick tube. (All MBs for the last 20+ years have a dipstick tube which extends all the way to the bottom of the oil pan.)
I can't recall the exact values, but the topsider was *more* effective than the drain plug, leaving about half as much fluid in the pan. I believe the values were something like 300ml for the drain plug, 150ml for the topsider.
This should not be a surprising result. MB designs their cars to be changed using the topside method, and in fact this is the recommended factory procedure, according to Mr. Murphy.
There's certainly nothing wrong with Larry's overnite method, but I'd wager that 15 minutes with a topsider would extract more old oil. The key, of course, is to change the oil while it is *hot*. No arguement there.
Don't forget that a liter or so of old oil always remains in the oil cooler, and you can't change it out. Hence getting that last 100ml out of the oil pan doesn't mean you got rid of all the old oil.
Enough preaching for now. I can dig up the citations for George's experiment if anyone cares - the list is archived.
Larry - you commute from Richardson to Honey Grove? You are nuts!