Hi,
That intermitent aspect was the same with mine too, to begin with... some times they worked, sometimes they didn't.
The earlier sensor housings crack and suffer from water ingress and then condensation which seams to make and break the circuit within leading to:
"3285 - Sensor for Contact with Door Handle; Front Left
011 - Open Circuit".
If it's failed, it will again, as the cracks won't mend themselves. I'd look on it as more of a reprieve... don't strike it off your "jobs to do" list just yet and save the link.
In the attached link it mentions that Audi recommend all 4 sensors are changed if the fault occurs (which to me implies if one has failed, you have the "known fault" type and so the others wont be too far behind... as in my case to prove the point). I've just been tight with a cost of £76 a door and replaced each as it's failed. Only one more to go now and I'll have changed the full set, but in installments ;-)
As for taking it to Audi and insisting they cover it.... well I don't fancy my chances persuing a claim on a 4.5 year old car on external electronics, even if it is a known problem. The above link never did actually reference a TSB that could be quoted - if there was something in writing a TSB etc, an admision of some sort, then maybe, but even then I suspect only if it were just out of warranty.
Ian