Valves, Checking
WARNING: This page is about a different car, the 2016 Volkswagen Beetle, 2015 Volkswagen Beetle, 2014 Volkswagen Beetle, and 2013 Volkswagen Beetle. 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.