S4 timing chain - how much should I worry

Looking to buy a B7 S4 and the internet is awash with tales of timing chain / tensioner failures and horrific costs to repair (if it doesn't goose the engine). 

If I took it all in I'd just walk away and never buy one however I need to put it into perspective . . . 

I'm looking at cars with 60k - 80k on the clock and at the moment am steering away from anything approaching 100k. I'm looking for evidence of the cars being on a 12 month service cycle rather than 24, main dealer stamps and with regular oil changes. 

What's the official Audi line with this, is there a point where they are saying the chains should be replaced or simply, well maintained with regular oil changes they'll keep going for ever??