Hi, I have a 2006 TL. I am losing about 8 lbs of tire pressure each week. I was told by my dealer that two of my tires had bad bead seals and 3 tires had a bad tire pressure valve stem. They wanted to replace the stem including the TPMS at about $100/wheel. I just had them fix the tire bead seal and I am waiting to see how they do. Has anybody ever replaced the TPMS valve stem by themselves?