Thanks lads - the seals I wrecked were new! Used rubber grease too. Everything was scrupulously clean. Pistons certainly wouldn't push in with MY thumb pressure - had to use a G-clamp! As said, the pistons are not alloy - but rubber - Something I've not seen before (it's an MC16). Was wondering if the pistons swell with age - making refitting more troublesome than I'm used to?