My comments on that are based on what people said in car forums. As somebody who had sometimes used tires with no valve cap, I found that I had been doing it wrong. Yet when I looked for what I thought I remembered, I did not find that. So I think that I should rescind my thought about the valve cap importance.Reach4 : wouldn't the actual Schrader valve be the problem and not the cap?
A good valve cap does seal, but it looks like it might be the secondary seal.