ck42,

Highly recommend the MB antifreeze. Did you decide where the fluid was leaking from?

I normally do not use any sealants unless there is evidence of pitting or worse corrosion in the gasket seating area. The clamping pressure distribution around and between the bolt holes can be adversely affected by by a number of things at assembly, including how tight the belt is drawn by the alternator position adjustment. Too much lateral force can unload some of the fasteners, especially if they were not properly tightened. It also wears the shaft bearings and shaft seal out prematurely. With properly tightened bolts you only really need a continuous contact all the way around the joint that is at least 1/16th of an inch thick. The width of the good surface (no pits or gouges) can get thicker, but if it less than a 1/16th of an inch, I would use a sealant. If you use a sealant take care to use it sparingly and follow the manufacturer's directions exactly. Some require a thin layer on the gasket and the mating metal surfaces, some do not.

If you use a sealant, take an extra step or two checking the fastener tightness. As the sealant is extruded into the water way area and out the edges, the torque on the fasteners can relax. When all is said and done, the fastener toque should stay at the value you set it.

As for where to put the flush water in and let it out, I usually flush the radiator for a while and then close the plug on the bottom and flush in the radiator and out the block. Seems to get the big stuff out. Last time I did it I used the MB citric acid flush stuff too. (edit: If you use the citric acid or other flushing chemicals, the directions usually tell you to fill the system and run the car to normal operating temp for some period of time. When you do this you turn the interior heat on to flush out the lines and heat exchangers fed by the coolant system too)

Good luck, Jim

__________________
Own:
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

Owned:
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)