I understood where the leak was, but the source of pressure that causes the fluid to leak out really quickly is likely the pump. Shutting the pump off by cutting the belt (you can't do this because all your accessories run off the same belt) makes the situation a little less likely to have the oil just pour out. There is still the pressure caused by the elevation difference though.
I have never had the problem you are facing so I cannot offer any worthwhile advice. I would be inclined to take it back to the dealer though as a Mercedes Benz part installed by a dealer has warranty for something like 12 months and/or 12,000 miles. I would tow the car or flat bed it there and have him pay for the tow as it is clearly a case of poor workmanship.
Good luck, Jim
1986 Euro 190E 2.3-16 (291,000 miles),
1998 E300D TurboDiesel, 231,000 miles -purchased with 45,000,
1988 300E 5-speed 252,000 miles,
1983 240D 4-speed, purchased w/136,000, now with 222,000 miles.
2009 ML320CDI Bluetec, 89,000 miles
1971 220D (250,000 miles plus, sold to father-in-law),
1975 240D (245,000 miles - died of body rot),
1991 350SD (176,560 miles, weakest Benz I have owned),
1999 C230 Sport (45,400 miles),
1982 240D (321,000 miles, put to sleep)