Just to add...
You will need a T55 torx, not a T50, and guess at which point i realised this...?
I couldnt get enough surface area on the piston to tap it out with a screw driver or similar. However, a pair of waterpump pliers gripped around the very end of the piston twisting and pulling removed them quite easily.
Also, to try and fit the weather seals into their channel after putting the piston in proved somewhat difficult. There was barely any room to squeeze the rubber seal in without damaging it. So i opted to install the seal and its retaining ring into the channel first then stretched the seal over the piston and pushed it home.
Easy enough...