Bearing noise = toast. Not sure about the W210 fans if they can be serviced or not. I know the 126 can be serviced by drilling out a couple of rivets. My fan ran, but howled like a banshee. New bearings shut it right up and been fine ever since. 3.2V may or may not be enough power to break the motor free, assuming it actually is providing 3.2V. I guess you'll find out with the new fan.

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Current stable:
1995 E320 149K (Nancy)
1983 500SL 120K (SLoL)

Black Sheep:
1985 524TD 167K (TotalDumpster™)

Gone but not forgotten:
1986 300SDL (RIP)
1991 350SD
1991 560SEL
1990 560SEL
1986 500SEL Euro (Rusted to nothing at 47K!)