Bol D'Or Antidive o ring diameter

Does anyone know the diameter/thickness of this part? Looks like thats where my issue has been all along, and not the fork seals.
So, 1 x O ring and a new set of seals, and the F2 should be back on the road again.

Are we looking at the seal for the anti-dive case?
It’s part no.91308-mj0-003
Dave Silver has it listed at £5.15 inc vat
Regards Bif

If this is the right part number then this is the dimension;

91308-MJ0-003 O-RING — O-RING (49.4X3.1)

Should be under $7.00 aud for genuine one.

Ordered 2…one for each bike, plus a spare.
always good to have spares.