After constant ear-ache from the owner and dealer that sold it to him, hours of second-guessing my self and going around in circles the car is now fixed!

Turns out our "repaired" ABS ECU came back with a fault it didnt go with free of charge (even though we sent it back for further testing under warranty)! Renewed the ABS ECU with a brand new unit and faults instantly cleared even with the original rotation sensor fitted.

Important lesson learned and the last time i'll try and do a used-car dealer a favour by having an ECU "repaired" and saving him a few quid - its new unit or no unit from now on!!