The website wasn't too helpful. I called the company but the are closed right now. You can check out the website yourself if you'd like www.slime.com or I did leave a message, they may call me back. I will put an update on both the auctions when I have an answer for you :-)
Can't update, I waited too long. But if you read this the company called back and said that all the caps are plastic lined. What they found out is this after a long period of time the metals of the cap and valve can fuse together, with any valve cover.