Clutch slipping even when fully tightened

[Acksaw]

Hi all, I have a one meeting old TLR 22 and when I try to set the slipper before re-using it I cannot get it to stop slipping even when fully tigthened. I found online that some springs were smaller but I've mesaured mine with a vernier and it's 12mm so it would seem the right one...

Any ideas? I've tried flipping the pads already and rebuilding it several times