Based on what I've read, I'm assuming the head gasket is blown. If so, you now have coolant in places it should not be to include the lower area of the motor. The crankshaft bearings may have been damaged by the coolant being introduced into the oil.

From my way of thinking, it's more than just changing out a head gasket. The bottom end will need analysis and the entire motor will need to be cleaned to remove the coolant. In the end you could be looking at rebuilding top and bottom.

I'm personally leary of used engines. Just how used and what is already wrong or about to go wrong with it.

My 2 cents.

__________________
Mike Murrell
1991 300-SEL - Model 126
M103 - SOHC
"Fräulein"