I've pulled many small items with my 76 240D on it's bumper mount hitch. The guy I bought it from was towing a 17' bass boat with it!
I also have a bumper mount hitch on my 300D, but have only towed the empty 8' flat-bed trailer a few miles with it (wife doesn't like me to tow things with her car ).

I would like advise on this as well... Am I doing something dangerous with the bumper-mount hitch or will the bumper handle this weight without problems.
What is the maximum weight the bumpers will handle safely?

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William
76 240D (W115) - 550K miles
78 300D (W123) - 200K+ miles