I have a relatively new twinhead on my Topeak pump (6 months). It worked fine at first but now leaks when using it on presta valves. Specifically, when pumping, air escapes out of the schrader side. Its not that big a deal because air still goes into the tire, and if I put my thumb over the schrader side, I get a pretty reliable pressure reading on the gauge. Its just annoying. I made sure all the caps are tight, and I happened to have twinhead rebuild kit so I replaced all the seals; still it leaks. It does not leak when using it on schrader valves. ANy other troubleshooting tips would be appreciated.