i have the insert, was one of the first to contact dan about this issue on the cats. the heat still messed with the threads and melted them BADLY. this season i wanted a permenant fix, and was going to put new oil jugs in. but, i called Kelsey at Rk Tek, talked to him, and bought his cap for the fix.
the cap is metal and only needs to be screwed on once and you NEVER HAVE TO DEAL WITH WARPED OPENINGS, OR MELTED THREADS AGAIN!!!
the machined cap is super high quality, and has ultra sharp threads that actually recut melted threads, if you work at it slowly, making sure the cap stays level as you "work" the cap down the threads to seat on the gasket on the new cap.
both products together work well but, the metal cap is THE fix. Ski