My folks late 89 740GL sedan has two recurrent problems with the ABS. When the car is moving slowly (say, through a car park at less than 10Km/h or coming to a stop) the ABS activates and the brake pedal goes hard. This lasts for a couple of seconds before all returns to normal and only occurs at slow speeds. The front sensors have been cleaned on a regular basis to address this problem and usually it helps but now it is not making any improvement.
The other problem is that sometimes the ABS warning light on the dash lights up. It will go off with all the other lights when the car is started but then come on shortly after. Is it possible these two problems are related? Could it simply be dodgy sensors? This car has always had ABS problems but I've never had a problem with ABS on my 91 940.

Any input would be appreciated.

Thanks
Brad