On a bmw the ABS system is made up of a reluctor (pick up ) ring (expanded with heat and to contract tightly when cooled , not bashed into location ! As I’ve seen done ) , and a sensor with both on every corner .
Over time the metal under the ring rusts out and expands the ring so that it either rubs the sensor , or is enough out of concentric to throw the fault .
A cheap fix is to try an M6 washer to space out the sensor a mill , but it’s delaying the enivitable if rust is heavy .