Optimus 45 tank pressure leak

Either that or not wanting to end up in a potential fireball.
We always have a stove in the back of the car and frequently stop for a brew. You can get odd looks as well as triggering remeniscences of simpler times when sights like that were verging on normal.

I tend to lay the filler cap on its back and with the blade of a small scewdriver set radially on the old seal, give it a couple of taps with a hammer - just enough to break the rubber. Do that 3-4 places around the seal and prise it out in pieces. I have heard others talk of burning them out but the screwdriver and hammer works fine for me.

 

I have gently warmed the gasket with a small torch (flame), they become pliable for a bit.