If splitting the caliper body it requires 2 seals not one.
Put Powerhouse-uk Brakes into your search engine,then bike brakes drop down box,then select brake caliper seal kits then Yamaha seal kits, as said £19.99 complete kit without pistons, the two seals next to the bleed nipples are for the caliper body. You only need to red rubber grease the face of the fluid seal after fitting into bore then the lips of the dust seal before inserting the piston. Copper grease will knacker your new seals, the ceramic grease has been designed as it contains no metal fragments to effect A.B.S systems on cars etc but is a bit more better looking than copper on your caliper & does not effect the braking surface of your pads if it gets on them.