Final update from me on this one. I have 100% of the repair covered but this decision was made on customer loyalty based on the fair list of VAG motors I've owned and had maintained within the group over the years.
Audi are firm that this is a paint reaction to do with the zinc treatment on the panels and isnt perforation thats covered under the 12 year corrosion warranty. Therefore its covered for 3 years. Can't say I am happy with that; but I am sure its technically watertight if you challenged the terms of the warranty.
From my experience here, my advice would be that if you have this issue and you wish it to be sorted; you should get the 70% good will repair without much fuss, (provided the areas arent previously painted).
Anything over and above that you have some negotiating on your hands and brand loyalty appears key to securing this.
I was advised that if my lasy service had been done within the group it may be looked upon favourably.
Therefore; I'd reckon if you service yourself or use a trusted independant; the net difference in your costs will more than likely outweigh the gap between the 70% customer good will settlement and the full amount; taking into account the franchise labour rates.
I'm happy with the outcome; although I got mildly irked when I was advised that Ada had no record of being serviced by Audi (its actually about 50% main dealer/indy split - but this is due to the private plate and it also comes up as Little Tank for a period as its Mike's old plate); and there was no evidence of my loyalty to Audi!
Due to the above; my house moves and the last 3 Audi's I've had being lease cars - there was no record of the near double figures of VAG automotive products on my driveway in the last decade. Bit odd, but hey ho.
The moral - if you can be bothered with a bit of negotiating; have had your car serviced by Audi, or can prove brand loyalty - I think they will be very accomodating with you.
If your car hasnt seen an Audi garage since it rolled off the forecourt - I think 70% is your maximum contribution; so you are talking ~ £200 customer liability. If you have these bubbling areas and intend keeping the car a long time - they can only get worse!
It's worth noting that I found Audi Customer Services very helpful, courteous and professional throughout.
Audi have records that I'm a member of this forum too! I think this will be linked to my hinge cracking claim when I quoted the club and the campaign code. As stated previously, I deliberately kept away from discussion about the forum in this instance. The advisor mentioned it 'in conversation' today. Thank you Darren!!
Hope this helps anyone now or in the future experiencing this problem with their A2.