Originally Posted by a.k.a

first port of call as they are easy to get at are all the connections around the servo and bottle, there are quite a few including under the servo itself. Pop them off and clean the connections, use a electrical spray rather than wd40 and also give them a wiggle once reconnected.

If that does not sort the problem then start on the sensors in the hubs and the connector from them to the main loom. Start on the fronts first as they get the grubbiest.

I doubt its the abs ecu or assiciated fuses, but if all else fails these are above the pedals.

Good luck/ I had a similar problem and it was a bad connection between the front sensor and where it connects to the main loom, dried out and gungy.