While getting the car ready to come out of winter hibernation, I was checking the air in the tires. After taking the guage off the valve stem on the front tire air continued to leak out of the stem. I could see no dirt in the stem. The center pressure pin popped up the way it should, but air continued to leak. If I pushed the center pin slightly to the one side I was able to stop the leak. I do not want this to become a major problem on the road. I have stock wheels on my 2003. I realize that the valve stem is probably bad, but do I need to remove the tire from the wheel for a fix, or can I replace the stem by unscrewing it from the wheel? Recommendation? Thanks in advance.