My motor unit had suffered with corrosion and one of the pins (19) had eroded away, replaced it with a used unit, same part no 1U6959802D but the door mirror and locking motor don't work, continuity checked the wiring from the motor unit to the mirror disconnect and to the door lock, all good, applied 12v direct to the mirror and the motors both move & the lock motor runs, put it all back together, did a VCDS scan and cleared the previous codes re-scanned no codes but still no mirror or lock motor ? however I did notice on the scan when I first got the car the subsystem 1 was,  Subsystem 1 - Part No: 1U6959802D  Component: 4Q Tõrsteuer.FS KLO 0004  Now with the replacement motor I get this,  1U6959802D  3Y Tõrsteuer.FS KLO 0004  What's the difference between a 4Q & 3Y ??

If the motor pins have corroded it's more than likely that the terminal in the mutiplug has also corroded. I had this with mine and had to replace both motor and door loom. I have spare door lock, window motors and looms for all 4 doors now as they are the Achilles heal of the Mk1 Octavia.

I fished the remains of the pin from socket 19 and it looks good. Pin 19 is a supply from fuse 38 and that is good so I can't see it being a loom/connector problem, it was the difference between a 4Q & 3Y I was wondering about ? As far as I can find the 3Y is the saloon & 4Q the Combi ?

Have you also checked the wiring between the car and door in the rubber boot as they are prone to snapping in there? I have a vRS hatchback window motor in my tdi elegance estate and the loom and worked first time. I have also heard of the ccm going faulty. It's under the dash driver side.

If some of of the corroded connector pin is still present and the PCB is not corroded, it can be repaired as follows: 

Remove the PCB by digging out the soft waterproofing around all the connector pins with a small flat screwdriver then carefully push them individually with a pair of pointed pliers towards the PCB to break the water proofer bond with the plastic case. Once all these pins are released the PCB can be slid out of case. Push the  defective pin, which has a right angle bend, forward to expose it on the connector side of plastic plate. It does not need to be the same length as the others to make a good connection. The harness connector may well have a pin open circuit inside the connector as well as external corrosion. I repaired this by hardwiring directly from PCB through the motor control case and onto harness wire. Crude but effective. These units are becoming quite rare and expensive. I was recently quoted £50 for one!