You need some better diagnostic work. If the leak is coming from under the pump, I do not think you have a freeze plug there to my knowledge. The pump cover, shaft bearing and impeller assembly screw into the pump housing, an aluminum casting machined to house the pump impeller and mate to the block. The pump cover seals to the housing with a gasket that can get old and fail, and the housing seals to the block by a gasket too.
While it is uncommon for the gaskets to just fail, it is possible your car is not running on its first water pump and someone has damaged the sealing surfaces. In this case it could be the water pump housing to block or pump cover to housing joints that are leaking.
At any rate, you need to find where the leak is coming from and there are various techniques, including adding flourescent dye to the water and shining a black light on the block to look for signs of weeping or leaking.
Once you know what the problem is you can explore fixes. 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)