By snooping around on the net looking for a place to buy the common screw-on stem tool. Which I found it at Pep Boys for $5. But that kit is a real savior if you don't have a tire machine handy. Anyway, I was at my buddy's shop today and I wanted to yank that stem out and seal it- and of course it broke right off. Rubber rot all around the base. So I used his tire machine to break the bead and put a new stem in. Turns out ALL the stems were shot, so I did them all, and rebalanced all the wheels. Then I remembered seeing something on the net about a huge recall several years ago involving cheap Chinese valve stems that rotted quickly and caused leaks/accidents. Sure enough, the numbers on the bottom of the stem were those that were recalled and the time line was right. So if you did stems 3-4 years ago, go out and bend them over. Look for severe cracking- and if so change them out.