Seal for fuel cap

All done now, will test to see if it works when the rain stops!
Thanks Bif very helpful and, apart from the cracking sound when the one way valve cap came off it was all quite straightforward.

Like others, I am trying to fix my dried up gasket. I modeled one and printed it with TPU and it worked well but didn’t last due to the ethanol. Someone mentioned getting some made if they had the STL. I’ve attached some images.

I’m tempted to buy the VF750f Chinese cap and use its gasket but want to make sure I’m ordering the correct one. Can someone provide more information about them please?