Go to the nuts-and-bolts section of Home Depot. You will find a selection of extra-long nuts (around 1 to 1.5" long). I tried to draw a picture of one so you know what I'm talking about...

They're all imperial sizes (nothing metric), so I bought one that was just slightly larger than what I needed for the rear axle drain plug. It was around 49 cents.

Use a grinder or a file and file down 3 of the 6 sides of one end of the nut, so that it will fit in the hole in the drain plug.

You can now insert this nut into the drain plug, and then turn the nut (and drain plug) with a wrench or with a standard imperial socket.

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1989 250TD Wagon 5-speed, 160,000mi ::: Dark gray metallic / black cloth
1984 190D-2.2 5-speed, 287,000mi ::: Silver-blue metallic / black MB-tex ::: SOLD