ABS light on 1993 E280T

Hey all,

I have a problem with the ABS on my newly acquired E280T. The problem is similar to the problem described here:

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1. Start car, ABS system passes all diagnostics and light goes out.
2. I drive for about 1/2 Km, and ABS light comes on and stays on.
3. I stop somewhere for about 10 mins.
4. I start car again and set off, ABS light does not come on even after many miles, BUT when I brake the ABS cuts in at about 5MPH irrespective of the road surface conditions.

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I read that a good first try would be to clean all speed sensors on the car, and check whether the problem persists. Does this seem reasonable?

Do I need new sensor retaining bolts if I take the sensors off the car, or can I just leave the sensor in place while cleaning them?

Thanks,

-- Rien