Hi first post here, just picked up my 2.0 TDI sportline yesterday !
A couple of quick points on screens, until about 3 weeks ago I worked for the manufacturer (you obviously know who they are). The A3 is a massive contract for them as they supply the full set of glass which is pretty unusual in the industry, it's normally a mix for cost reasons. Didn't work on the technical side but found out enough about the processes and products to last me a life time.
The stress fracture is likely caused by one of a couple of things, bad fitting in the factory with resultant pressure on the panel and crack, out of spec windscreen (I know the people on the lines so this is a definite possibility I'm afraid) which causes pressure in the appeture, impact (not covered by any warranty) or large temp changes. The last I've only ever seen in Scandanavia where 6 or 7 inch cracks seem pretty common and the regs on them are far laxer than here despite the huge safety culture.
A manufacturing fault will normally appear due to delamination rather than pressure and appears as a milky white patch on the screen where the glass and the PVB interlayer have separated, this is very serious and should be replaced immediately for safety reasons! if it happens there will only be 1.5 - 2 mm of glass between you and the road, it will also probably break into shards as the interlayeri is no longer bonding the pieces together.
Most cracks are fine as far as impact resistance goes (unless they also cause delamination) so not a safety issue appart from visibility.
I was surprised to hear someone got an Audi branded part from Autoglass as that's normally illegal unless they bought it from a dealer which I've never seen them do....
There are in fact three types of part (they won't like me telling you this) OE (Original Equipment) which goes to manufacturer and is first quality (normally), OES (Spares) which go to the dealer network and AGR (After-market Glass Replacement) which goes to the likes of Autoglass through the company's wholesale network.
OE and OES are logo'd and normally the same but OES tends to include a fair number of OE parts that weren't quite right with light scratches etc that have been reworked and passed after re-inspection, AGR is either non logo or has the logo removed by laser (not always pssible with certain inks and etching chemicals) and produced to the same basic specs as OE but they allow a higher number of faults than OE (which are uber tight for VAG) but generally I'd be happiest getting it fitted at a dealer or insisting on OES glass bought from a dealer (OES is not available anywhere else) as it's much more likely to be first quality.
Even if I had to fit AGR I'd insist on the original maufacturer glass as a lot of third party glass especially from China is now on the market and is normally reverse engineered from cars themselves rather than produced in conjunction with VAG, I've seen some right horrors here!
If you are getting it replaced ask to find out what options are available as you could get glass that's ready to fit a rain sensor or has visible VIN plate etc if you don't already have it. A lot of different colours are also available (fancy blue or bronze rather than green?) and dozens of combinations of shade strips in various colours and depths (can't remember about max depth on this in UK tho') also you can get the thermal reflective glass, just make sure this is done by the interlayer rather than a coated windscreen (like Renault use) as the coating on the inside of the glass is Platinum based and blocks signals to GPS and mobiles etc.
hope this helps.
