It was probably me who posted the seal details
I can't remember the O ring size, or where I got them from! It was a while ago as you say. I measured the old seal with digital calipers and got all sorts of varying thicknesses (worn out basically!), so I took a punt on a size and it worked out perfectly.
The good news is I bought about 10 of them I think, so PM me your address and I'll send you one. In the meantime I will try and find my old post with the dimensions.