Ara t.,

The plug you mentioned on the driver side is one of four access holes for the cooling system. I believe two are plugged, one is used for the temp. gauge sensor & one for the heater hose outlet just behind the oil filter housing. It is extremely tight. The drain plug you want can be accessed with a socket/wrench on the passenger side forward & above the starter bracket.
It may be a pain to get to with things in the way, but that's the one you want to remove. Paul.

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'84 300CD 290,000