I have recently bough an A6 Allroad. I changed a front air bag as soon as I purchased the car. When parked overnight etc the suspension doesn't drop at all. But when I'm driving you can hear the compressor cutting in and out, running for a minute or so at a time. Does this mean I still have a leak??

 

Not necessarily, The car will always be adjusting it's leveling system so it uses air once the psi drops the compressor cuts in again. If you want to determine whether there may still be a slow leak park on a level pad, turn the car off and put it in jack mode. This will isolate each corner so if there's a leak, the system won't correct and level it out. Check next day and remeasure the height of each corner. A sag will usually indicate a leak. You may want to do this at level one, then level two to ensure the leak is exposed. Sometime leaks can be pinched off at different levels but not others. Over all uniess the compressor is running often it sounds like it could be normal.