Ordered a service kit which I've gone to fit today. The yellow foam rings that I assume should replace the white foam rings that are in there already, are a different height. Have I got the wrong kit?
I had the same problem.
A quick search revealed the black ring that comes with the kit goes in with it. You need to remove the grey top seal to fit them though. Or you can do what I did and just clean the existing foam ring with IPA and replace.
Mulletus Maximus is the man, and absolutely correct as I've just discovered.
I know I'm answering my own question but it may help somebody in the future.
The black ring is an oil seal but therefore creates a little more stiction if fitted, I'm gonna clean out the white foam wiper and fill it full of enough redrum to drown shergar, then put new grey wiper seals in.