Well my ASC and ABS lights now only come on when the engine starts and go off after a second or two as they should!
Here is how I did it.
Disconnected the battery.
Jacked up and removed front offside wheel.
Turned steering wheel to full left lock to get the best access and then I found it easiest to lie on my back with my head and shoulders under the hub.
Wire brushed the two mounting bolts clean and then tried to get the 5 mm Allen key into the bolt heads, it refused and I had to clean out the bolt head recesses with a screw driver then gently tap the 5 mm Allen key into the bolt head to ensure a proper fit as I didn't want to chew the bolt heads.
Both bolts removed easily without the need for WD40. The sensor actually broke up when un-screwing the bolts, there are two metal inserts bonded into the plastic sensor body which the bolts pass thru, both these inserts came away from the main body of the sensor. In other words there was no way the sensor that came out would go back in!
Sensor was stuck in the hole and had to be pried lose then it just dropped out.
Cleaned up the area around the hole and wire brushed the mounting bolts clean and greased them up when I put the new sensor back on.
The most difficult thing was squeezing the rubber mounting bush on the cable into the support bracket bolted to the hub.
Refit wheel and torqued up bolts and reconnected the battery.
Lights stayed lit until I drove the car 50m.
All clear, no faults, tranny shifting fine.
Job done by myself for a total cost of under £100 inc diagnostic fee.
Andrew
PS This method of checking which wheel sensor is defective by measuring the resistance of the sensor is rubbish. Both the defective sensor that I took off and the new one had a resistance of 6 Ohms! So in other words I couldn't prove the diagnostic check!