Valves, Checking
WARNING: This page does not describe the selected car, but rather 6 other vehicles, including the 2018 Audi S7, 2018 Audi RS 7, 2017 Audi S7, 2017 Audi RS 7, and 2016 Audi S7. However, it is still accessible from the selected car via links, so may be relevant.
-- Check valves at stem and seating surface for traces of wear.
-- If there are clear traces of wear, replace valve.