Hi Jonathan I had one very similar, we also have Autologic and Lawrence was doing his best but without any results. These do also have a problem with water ingress up the wiring loom to the ECU, they are always worth checking, our one had a rare electronic thermostat (Automatic) which leaked internally and pumped water up the loom into the ECU. Talking to our local VW tech he also said they are capable of pumping water up from the Lamda sensor all the way up to the ECU as well, they as a Dealer have seen a few of these.

I know yours is diesel but it is worth a look. I wish I had after 2 days of head scratching. Fortunately our one the water stopped at the multi plug and did not enter the ECU so after cleaning all green terminals the car ran perfectly.
John Kennard.