I ended up fixing the one on my 300SD by drilling and tapping the ball inside the bushing (straight down into the "top" of the ball) and then putting a machine screw through the bushing with a washer to keep it from pulling through.
It's held up for a year so far. I just couldn't stomach the ~$250 price tag for a new wiper transmission, and haven't been motivated enough to try to find another vehicle to source the bushings from, since MB doesn't think we need to be able to replace them.

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-Josh
Testing the cheap Mercedes axiom, one bolt at a time...