Thanks Euan, That's just teasing
But yes, I must have missed this picture it in the spare parts cattle dog (or it's on page 13, which I still don't have!).
It does confirm that my seals are out of original specification as they measure over 2" in external dia. From Andrew and Lynn's posts the sealing comes from them being squashed laterally. Given the material, I'm guessing that this 'squeeze' will be minimal so the thickness is what I need to work out.
I've now just got to find a company to cut them.