Steve, I believe the brushes are NOT available as an MB part. I'd remove the blower assy., check if the bushings are "egg- shaped", if not; sand the commutator, pull the brushes and head off for an electric motor shop in St. Louis with them for a "closest match" and carve to fit. Some one may have a source and will chime in. How's the corn doing around Scott this year...high as an elephant's eye?
The Golden Rule
1984 300SD (bought new, sold it in 1988, bought it back 13 yrs. later)