Over time the rubber seals at the end of the valve and the rubber seals on the valve cores get torn or become brittle and you need to replace them. Might as well go with the original, Stans. These work great and are a resonable price. In my experience they work on all rims.
Bought these valve stems because my Dura-ace C24's stems did not have removable cores which makes all the difference when applying sealant into the mounted tire that is beaded into the wheel. Stans valve stem was the perfect length and shaped the way it should be to fix into pista air chucks. Thanks, now it's simple to add air or sealant to my Shimano tubeless wheel set.