not saying you shoul do this to a benz, but my old f-100 had a leaky plug on the rear of the block, under the bell housing. i used alumaseal- the ground up aluminum in a tube. it worked great. I have never had luck w/ other stuff(barsleaks, etc) but alumaseal has even fixed a head gasket for 20k+ miles, for me.
I also have repaired a radiator with a fist sized hole thru it using jb weld. It worked long enough to replace it.(A few months) dont jump uni-bodies. they flex too much on landing. took me twice to learn that one
If you plan on keeping the car, your best bet is to fix them right, however.