I took my car to the shop to have the valve covers replaced a little over a year ago. Since then I have only put 4000 miles on my car. The valve cover is now leaking again, and the shop confirmed it was the valve covers. It's not leaking oil, just a little steam coming from behind the engine on the passengers side. But you can smell it when you pop the hood after driving it for awhile. Will I break the bolt maybe by tightening it? I have a torque wrench I was going to set it at the proper torque spec for valve cover bolts. I just hear they are 1 time use bolts only. I haven't even tried to negotiate to have the shop do the labor for free, their policy is 1 year warranty on work done.

 

Your leak may likely be from cam tensioner seals or cam seal, if not from valve cover.
These are multiple common leak joints on the A6. So if the shop just changed valve cover gasket, then they didn't adddress all the potential leak joints.
Valve cover bolts are not 1 time use bolts. Torque level is relatively low. About 7 N-m (5 ft-lb), I think. Don't over torque because to don't wnat to strip the threads.