Rear brake dragging

Advice needed. Please read through and comment if you have any informed advice on what could possibly be the issue here.

I've the 2.0l quattro TDI and have an ongoing problem with the off side rear brake dragging. This obviously destroyed the new disk and pads I'd fitted the previous year in jig time.  

Last month I replaced the entire braking system from each wheel arch. New calipers, disks, pads, and Flexi hoses. Thoroughly cleaned all carriers, lubed slide pins with appropriate grease ensuring pins were free and unobstructed then carefully reassembled and bled brakes at each corner. 

Everything working great with the exception of that rear o/s which is STILL dragging and driving me to drink. I've a cheap VW specific scan tool which has identified both rear wheel sensors are shot and a further fault indicating an ABS module problem.

I'm no mechanic but I'm fairly competent with the spanners and would love to resolve this myself before taking it to Audi. Anyone ever had similar issues like this? Any informed advice would be much appreciated.