To finish the thread, yes, it was the freeze plug and Enrique replaced it, the thermostat & radiator cap for less than $250 in labor. I'm very satisfied. Thanks to all.

Richard

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87 300e (white/black; amg body kit)
88 300ce (red/cream; amg body kit)
93 300ce cabrio (white/blue/blue top)
93 300ce cabrio (black/grey/black top)
98 ml 320 (totaled @ 137,000 miles)
99 clk320 (black/grey/black top)

that sure is a strange looking freeze plug in that pic. why does it have a nut shape in the center??? for turning???? hmmm u can ask the dealer to send a pic of the leak in action. the more you understand them , the more confident you can be that you have a fix for your money. if it is along the engine below the head , they could take the pic from below. casting, soft, or (freeze) plugs can be replaced individually. there is a plug offered by dorman that may simplify things. its metal, and you use two wrenches to start it. then you tighten the brass capnut. access is the key to success in these repairs because you have to tap in one side of the old one to spin it perpendicular before grabbing it and yanking it out. that is if its a standard core plug . there is also ,in some cases, the possibility of putting an engine heating plug in place of the one you remove.a block heater, then start your benz in freezing temps. i have been asked to stay late and get freeze plugs changed, at the expense of putting me on the hiway after dark in the snow. you can bet we had some expansion type plugs used in those instances to do us all a favor. huge time saver and debateably more reliable. NOW, if its a bolt, you might remove it, measure it, and add teflon sealer to it before installing and retorquing. stretch bolts need only be replaced when they are too long!!!! malpractice believers always sell new

Yes these are bolt in frezze plugs. Just for others looking in on this old post .You can get them just like a large wall plug Like runbber with a bolt going through it you lock it up and it expands .