I no this is not what you want to hear but her it goes.
I have been burning only one rave cap on one of my engines and have put it down to the fact that the rave valve port is worn to the point the hot gases are getting passed the rave valve and melting the cap, i have replaced everything a couple of times and it still happens. I'm keeping it going until winter when i will swap the cylinder for a new one and hope that will be the end of it.:cheers: