After many weeks (and nearly £2k poorer) I have finally got Project Spa back, error free and running like a dream! The boys at Garage Bavarian were very persistent, working their way through the possible issues (including replacing cam position sensors and eccentric cam sensors for OEM), but the cause seemed to be low oil pressure due to a damaged oil filter basket. That was replaced, oil was flushed and oil pressure was bumped up. Hey presto, no VANOS error codes! Drove it for an hour to make sure all was ok and it us running better than ever. Checked to code reader a few times and all is clear. Result! 108s are now back on, car is cleaned and I will get it up for sale in the coming days.
Expensive but worth it - I didn’t want to sell it knowing there were still issues with this.