Rear Brake Caliper Fitting Seal

[lukeydoo]

There is a tiny rubber seal that fits in the rear caliper as indicated and I cannot get the new seal in from the inside at all - I've already ruined one seal already! How do I fit it?!

[Bossworld]

Struggling to tell from the picture but if it's the one I'm thinking of, you need to use a socket to grip it and gently tap it in without tearing it.