Tony T please except my apologies for the delay in replying, e bay search just simply putting in a search for 'O' rings. shore 70 hardness, don't buy made up kits it is Much cheaper to buy by size.
Inside diameter X thickness. IE. 20 X 3 mm. for example.
Waiting for new computer, this one is packing up , hopefully back soon.
All the best.
Geoff.