O-ring selection and replacement

So I need to replace the static o-ring seal. Some background reading: Parker o-ring handbook. Look a section 5. Useful application info - but of course it's Mercan ie imperial units.

Barnwell o-ring catalogue including piston groove dimensions.

George Lodge Direct website.

The static o-ring seems to have become shredded, presumably during insertion last time round. This would have leaked like a sieve if I'd tried it.

The dynamic seal on the piston looks fine. 

Thin o-ring:

• Bead - 3mm diameter
• Piston - 110mm diameter
• Groove - 105.5mm diameter (this is the required ID dimension) 

Fat o-ring:

• Bead - 5.5mm diameter
• Piston - 110mm diameter
• Groove - 100mm diameter (this is the required ID dimension)

So I require an o-ring with an ID of 105.5mm and a bead diameter of 3mm.

Like this from George Lodge Direct Consider it ordered...