The Brumby's internal rear view mirror has recently become loose. The mirror's ball joint doesn't hold a position, so the mirror flops down when driving along.
I've unscrewed the mirror's arm from the ceiling and had a gander at the assembly, but there aren't any visible screws to tighten. The mirror is firmly attached to its black plastic shroud and I reckon if I try and prise the mirror out with a scewdriver I'll just crack the glass.
I'd like to re-tighten the ball joint if possible, but I can't work out a way to do it.

Does anyone know how to fix this problem?