I put the 0.9 cap on maybe a year ago, so its not old. It has worked fine in that time.

The new radiator came with a 1.1, but it felt a bit cheap so i decided to put the 0.9 on my new radiator because i feel like its a better quality cap.

So i will stick with the 0.9 i guess. If my 0.9 becomes faulty i got a fresh 1.1 ready to use.