Mine gave me over 200k miles...
.. then one day the bearings went bad and made a horrific noise at startup, so I simply disconnected it. The cost far outweighs the benefit at this stage of my 300E's life. I don't even think the earlier 300E's (or any other MB for that matter) had this pump as the 300E shop manual from '86 refers to this pulley on the serpentine belt path diagram as a "deflector pulley".
What year did MB add this A.I.R. pump to their engines?
'91 300E, 207k miles