I've put numerous valve stems in the front of my zero turn in the last ten years. For whatever reason about every other year they'll start leaking where the stem exits the wheel. Still all original front tires, just a boat load of valve stems. Slime is pretty amazing for a temp fix on large tires. We laced up a 4" slice in a sidewall with a cordless drill and some wire, and 3 bottles of slime on the trail one time. Held 20 psi long enough to get back to the parking area, that was on a 40" super swamper.