I ain't no expert BUT if you drive with the ABS light on it kinda implies that the ABS isn't working. UK Insurance companies are now taking a very dim views of this and if they can prove that in the event of an accident that the ABS wasn't functional, thay might be inclined not to pay out. Not to mention potential police prosecution. Just a thought.
Anyhow, I have had both ABS+ASC lights on constantly, beginning last week. Took car (520 E39 1997) to dealer yesterday and, contrary to meddling with the sensors, they've replaced my disks and pads, plus a wheel bearing. Warning light problem now fixed. No sensor cleaning or replacement. I'm collecting my car today and have asked for the old parts back, (seeing as they're mine!)
2 hours labour!
Might be worth giving the dealer a chance. They'll suss it out and let you know what it needs before actually fixing it.
Good luck.