I had that problem a couple of months ago....the surround of the head broke off, but still left a philips head, sort of button looking......the threaded portion has an "O" ring in a grove that does the actual sealing.....that big collar holds a locking device something like a star washer......you will be ok, there is just nothing to prevent the drain plug from backing out......

I drove over the weekend, and on Monday, went some 60 miles to the MB dealership, purchased the drain screw MB part # A 000 501 01 71, drove home (60 more miles).....then changed the plug and antifreeze......was changing my thermostat when this occurred ......

If you have Green antifreeze in your car....you should switch to either the official MB gold stuff....or the Peak Global version......while you are doing the plug swap.....

SB

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Diesels:
'85 300D, "Max, Blue Benz", 155K, 27.0 MPG
'84 190D 2.2, "Eva, Brown Benz", 142K, 40.2 MPG
'77 240D (parts car)
'67 Eicher ES 202 Tractor "Otto" (2cyl, Air Cooled, 30HP)
Gassers:
'94 Ford F-150, "Henry", 170K (300 Six) 17.5 MPG
'85 190E 2.3, 148K....Parts Car
'58 Dodge W300M Powerwagon (Flat Fenders) Less than 10 MPG