So my A6 4.2 has 100000 miles and I think I need to replace the stock sport shocks just from time. Anyone on here know when its recommended or if there is a certain Mile range that you are expected to do so. I am looking into doing the Koni Sport struts and shocks.
Thanks

 

The standard shocks on my 00 Avant were shot at 114k miles. I don't think there is a mileage range when they need to be changed. Just when they start to fail. Our 3 series has ~130k on it's factory shocks, and they're still tight.

 

The shocks wear out progressively so you won't notice the performance degradation that takes place over the years.
I would say that at 100k miles you are due for shocks, and you should feel a big difference once you have them installed.
While you are at it try replacing with Bilstein or similar shocks. Better than stock and they are rebuildable.