My Roval Control SL Specialized tubeless valvestem leaked at the o-ring. This was fixed by the shop (who had fitted new tyres) by re-taping the rim and using a conical-shaped gasket stem. Conical vs. Flat sealing surface a better design for sealing because the sealing force over surface area (pressure) with a cone is higher with a cone in the hole compared to a flat o-ring *around* the hole, but the cone is riskier to the structure of the carbon fibre rim because ithe cone produces higher bending stresses and splitting forces on the edges of the hole at the seating surface. The original design is less stressful to the carbon rim over time and is safer for the rims at high pressures and high impacts. The flat o-ring just needs a more attention to detail by the mechanic to fit the tape and stem o-ring to the rim tape without any ripples or bumps, for it to work as designed.