73MB280SEL

The auxiliary fan is susceptible to damage to the bearings over time. They sit in front of the radiator/airconditioning condensor and are subject to being bumped, pelted by water and debris from the road, etc. There are some threads that describe taking them apart and replacing/repairing the bearings. I just looked on Fastlane and the auxiliary fan for your car is $273. It might be worthwhile trying to take it apart as you have nothing to lose. When they have a bearing problem they typically won't move by pushing with your hand either, or if they turn they are very hard to turn.

Try a citric acid flush like the MB manual suggests. It may clean the rest of the grease and oil out. Good luck, Jim

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Own:
1986 Euro 190E 2.3-16 (291,000 miles),
1998 E300D TurboDiesel, 231,000 miles -purchased with 45,000,
1988 300E 5-speed 252,000 miles,
1983 240D 4-speed, purchased w/136,000, now with 222,000 miles.
2009 ML320CDI Bluetec, 89,000 miles

Owned:
1971 220D (250,000 miles plus, sold to father-in-law),
1975 240D (245,000 miles - died of body rot),
1991 350SD (176,560 miles, weakest Benz I have owned),
1999 C230 Sport (45,400 miles),
1982 240D (321,000 miles, put to sleep)