it's very easy. twist the end of the leather gaiter so as to get double thickness and just push it in with a knife/key or something

I cut the bottom of the rubber one off and used double sided tape to attach it to the leather one then just slotted it into place and put the plastic ring back on! If you started tugging at it hard it would probably come out but for day to day use its perfect and you'd never know thats what i'd done . Happy days!

Oh and cheers for the help everyone

Good stuff