BAC window latch mechanism how to get at it?
 

We had some windows installed by BAC a few years ago
(before their latest reincarnation that was discussed here).
Overall not bad, but one problem they didn't sort out
(and we eventually gave up nagging) was the latch mechanism
on a bathroom fanlight, which wasn't screwed on tight -and
wouldn't close if it was. This naturally got wobblier
with use and I was thinking I ought to do something...
but it beat me to it and gave up. The window is closed
and when you turn the handle to the 'open' position you
can feel that the left hand side is unlatched and the right
side still tight. Does anyone have any idea how to get access?
If you take off the latch mechanism, it's much like a doorknob-
you can see the socket the square shaft engages with and not
much else. The edge of the windowframe is well protected
by the overhanging edge of the frame on the outside and
the frame on the inside. Is it possible to (non-destructively)
pry out the glazing bead, and if so would that get me any further?

I'd be grateful for any suggestions ...

Leo