Removing tailstock barrel Colchester Master 2500 / Student 1800

Has anyone sucessfully removed the barrel from a Colchester Master 2500 or Student 1800? Looks to be dead easy, remove the handle, remove
the bearing retainer and slide rearwards having first removed the barrel locking mechanism.But there is the rub, I cannot get the locking mechanism out! There is a simple horizontal shaft with the lever mounted radially at one end, with an eccentric in the middle bearing on a piece with a key that gets pressed upwards to lock, and a cap head screw underneath tp prevent it turning too far.
I'm trying to sort out rotational play (between the 'piece with a key that gets pressed upwards' and the keyway on the barrel) so I can fit a depth dro bodged from a digital caliper, but if the play remains it will be twisted to bits !
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