I had the same problem with my stove leaking a slight amount of smoke at start up. I took about 1.5 feet of 3/8" rope gasket material and packed the void between the cap and tee. Use a flatblade screwdriver and pack it in snuggly and leave yourself a short tail so you can remove it for cleaning. I did this at the appliance connection as well and had to use an allen wrench to press the gasket material in place.
