Piston BS115 Viton 17.12 x 2.62mm.
Cylinder to valve block BS115 17.12 x 2.62mm Nitrile.
Breech seal (end of barrel) and Valve Body x 2 BS610 6.75 x 1.78mm Nitrile.
Valve inner seal BS007 3.68 x 1.78mm Nitrile.
To the best of my knowledge NBR 70 is suitable.