I Installed Slime brand (Auto Zone) inflation valve extenders on my RV-6 only to find one of my tires flat when I went to fly after about a week away from the hangar. The wheel pant settled onto the chocks causing minor/repairable damage to the fiberglass. My inner tubes have very stubby inflation valves, thus the extenders were used. The extenders are off now but will be briefly installed to allow inflation. I learned another local pilot had the same problem with his C-185.