No problems with valve stem failure in my Slimes at 125 PSI. However, the slime won't hold 125 PSI with a puncture; it will deflate to about 80 PSI and hold. I know this b/c it has happened a couple of time; the tire will deflate a bit with a puncture, and I will stop and try and fill it up more. If I get over 80 in there it will rupture the puncture until about 80 PSI or so, and then hold. 80 PSI is more then enough to get home on.