A friend of mine faileed inspection the other day becuase they said he had something wrong with the abs system on his 1988 300E. He said there was some sort of grinding noise like metal on metal when it was engaged. I'm not reall that familiar with the car but does this sound like something i could help him with or should he take it in?

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W126 1983 300SD 286,000 miles and ticking
Baby blue exterior Grey MB tex
Recent work:
Replaced air cleaner mounting brackets and heat shields
Replaced alternator, fan and power steering belts
Replaced positive battery terminal
Replaced negative battery terminal and cord
New Duralast Battery

My car needs work.