Joe:

Nothing will come loose unless you pull the lower bolt pin and the upper one a the same time. The upper inner bolt pin unscrews as one piece, the lower has a plug.

Use a new aluminum crunch washer under the plug -- if there isn't one there, that is why it is leaking. You can tell which one gets the washer -- it will have a flange and machined flat on the block. Use permatex on the other one. My brother left the washer out on his, helped with the oil leak. Big pain to replace on the W115, probably easier on the W123.

Peter

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1972 220D ?? miles
1988 300E 200,012
1987 300D Turbo killed 9/25/07, 275,000 miles
1985 Volvo 740 GLE Turobodiesel 218,000
1972 280 SE 4.5 165, 000 - It runs!