Zulubravo44 makes a good point.... I put together a Micromag with a classic valve probably 10 years ago now, and even with new O-rings I couldn't get 3 different classic on/offs to seal. Just for grits and shins I put in the only other one I had, which was an R/T on/off. It actually sealed, and I tested it when I got the rest of it put back together, and I'll be honest, it has the sweetest predictable trigger pull I've ever seen on a mech. I've had an R/T Micro, and I've pulled a ULT trigger as well, but this had the right amount of stiffness for just the right duration.