Looked again at the action, the gun belongs to a friend. There is no screw on the knuckle to act either as retainer to the pin or as anchor for the extractor cam. The cam appears to be one piece with the action knuckle.
I do not exclude rust on the threads as a cause for the sticking, however there is no hint of visible rust anywhere on this BSA and overall it is in excellent shape.
Failing pin removal it seems that bringing it back on face will have to be done solely via filling the hook.
Still would like to know about the that thread though, just academic like, whether it is left or right hand thread.
