most probably the motor jammed internally (seen it on other brands of cars). Your best repair would be to find another motor/assy.

almost any later than 1992 W124 will fit

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2012 BMW X5 (Beef + Granite suspension model)

1995 E300D - The original humming machine (consumed by Flood 2017)
2000 E320 - The evolution (consumed by flood 2017)