14-09-2018, 09:26 PM
Use your car more! Sorry if that sounds a bit flippant but the valve stems are lubricated by oil mist alone, if you only use your car occasionally and on short runs very little oil will make it to the valve stems. I guess some oils will have better clinging properties so will be less inclined to drain away between use than others, but the more use a car gets the better it runs in my experience.
Black Art Enthusiast