ABS faults are often to do with the sensors. Iron dust from the brakes can get attracted to the magnets, wires can crack, reluctor rings (AKA "tone-wheels") can fracture or come loose, connector plugs can corrode. It is possible to repair cracked tone-wheels in spite of what official channels may say. One just brazes-up the split with Sifbronze. As this is non-magnetic it doesn't really matter if the entire tooth gap is filled. Re-fitting involves removing the rust on the shaft and ring with emery paper then gluing the ring in place with anaerobic sealant then painting the tone-wheel with anti-corrosive paint. Such a repair is not really a bodge as it will normally outlast the car.

On some cars the ABS control box has a resiliently mounted circuit board inside. Unfortunately this resiliently mounted board may be soldered to rigid pins. The result is that after several years dry-joints can occur. Sometimes the cars Owners Club may advise on how to hole-saw the control box and re-solder the dry-jointed pins.

Note that with most control boxes on cars the golden rule of computing still applies. The rule is RUBBISH IN = RUBBISH OUT This is certainly the case with MAF sensors as the "brain" has no idea that it is being fed with duff-gen when dust burns on to the hot wire.

Good luck!

PS This might sound stupid but are all the tyres round? I jest not as many years ago I had a Leyland Mini that would vibrate badly at 50 mph. Up to 30 mph was OK and 70 mph was OK but at middling speeds there was vibration.

The wheel bearings, drive shafts and brakes all seemed OK and I think that I had the wheels balanced again but nothing could be found. In the end I discovered that the tyre that got heated by the radiator had become slightly oval! Grrrr!