I need to upgrade our door locks. The rear doors' Euro cylinders were no
problem - undo M6 bolt, turn key about 20 degrees, slide out.
But the front door - also upvc - is different. It's a Yale fitting but
there's no securing bolt into the cylinder from the edge of the door. Even
thought there's a hole in the right place in the decorative trim, behind
that a plate slides across when the deadlocks are engaged, so it can't be
bolted that way.
I thought maybe it was bolted from the other (hinge-ward) side so removed
the double-glazing-like beading from the stiles/rails, but the whole inner
panel of the door has been secured with silicone, and the panel covers where
the bolt head would be. So if it was bolted from the inside they would have
fitted the lock before assembling the door, which seems unlikely.

Any suggestions? Last resort is to get a locksmith to snap the cylinder and
advise how to fix a replacement. (I had a half-hearted attemt at snapping
but didn't want to end up with a bent but otherwise intact cylinder still
fixed in place).

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