As a piano technician I would have to say that it is *never* acceptable
to glue centre pins in place.  If the pin is properly tight in the body
of the component, gluing the exposed ends to the flange will merely
*lock up* the whole component and prevent proper playing.

The whole purpose of the bushed flange is to allow the pin to move
freely within it whilst keeping its host component relatively tight.
Loose pins suggest either worn  bushings or undersize centrepins.
Assuming that the bushings are okay, what is needed is a complete
re-centering of the action with next size up centrepins -- a fun job.

The fact that the action is only six years old does not augur well!

Roger Waring
The Pianola Workshop
Solihull, England