Adrian,
true it could be a sticky piston but if both discs and pads are changed why does it appear now? I guess maybe pushing the pistons back for new pads.
Worth checking as you say.
Yes I had exactly the same issues, which makes me suspect this is the problem here. If the discs check out on the run out check I would be even more convinced that a sticky piston was that cause. Remember that the old pads would have work to a particular shape (wedging) which may have been masking the problem, then you fit new pads and disks and then have the judders with low brake pressure.
