Paul, you're supposed to be able to pry the retaining metal that keeps the brushes in place and replace the brushes. You'll need a soldering iron to resolder the new brushes in, push in the backup springs then bend the tabs back over. You should do it before the brushes wear completely and the springs ruin the commutator.

Ace hardware has brushes, just not in the exact same length or cross section. Others have filed them to suit with no problems.

Of course you're not supposed to be able to replace the brushes. The MB paradigm has always been when in doubt buy a completely new unit. MB is hoping you'll give up and capitulate to buying a $300 part. However people have always found a way to fix these unfixable MB components. Just takes a little time and dexterity.

I do it because I enjoy the satisfaction of being a cheap bastard. However recently I had to cough up $300 for a new EGR valve, something one will never feel a benefit from but is essential for passing emissions testing. I tried like hell to find a suitable used part, but in the end had to give up and buy a new one. I have no idea why those things cost so much, they don't look like $300 worth of anything, and the car failed the emissions test anyway.

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'02 BMW 325i
'85 300D 450k
'93 190E 2.6 170k(killed by tree)
'08 Ducati Hypermotard 1100S 6k
'06 Ducati S2R800 14k(sold)