Have you thought of asking VW to get involved, purely as a research excersise?
Send them all the data, along with a full report and see if they can offer any ideas - you'd be surprised how keen they can be to solve a quirky one, just out of curiosity alone. I know Bentley have pulled in 10 year old cars before now when something unheard of has gone pear shaped, engineers can't help themselves.
Good luck.