Always use a new gasket - buy them from VW or Audi - its not a place to have a leak.
11nm + 1/4 turn - buy some new bolts whilst you are at VW - you don't need a tension wrench (as VW advise doing this job with the rear drive unit out of the car) - you need common sense (don't think you will get a tension wrench in).
Depending on the age of your car & mileage (and the last time your Haldex was serviced). If your car has done more than 30,000 km's I would suggest changing the Haldex fluid & filter at the same time. Could save an expensive repair down the track!
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