I've been trying to find where the water's getting out of my shower
cubicle. Access is poor, I have a little gap up the side and I can see
the underside of the tray, but it's too tight for me to actually reach
in there.

The problem is that water drips from somewhere near the wall, it's
dripping through the floorboards and wetting the plaster of the ceiling
below. It doesn't do it every time, and I can't figure out what makes
the difference. There are no cracks in the tray, and it doesn't look
like the water is escaping either from the pipes, the fittings fittings
or the drainags system. This really only leaves the tiles, the grout
and the silicone sealant. The lowest two rows of tiles above where I
believe it's coming from were loose, so I took them off. Sure enough
the wall behind was wet, so I dried off and re-stuck the tiles,
re-grouted and applied silicone along the egde of the tray to make
sure.

All seemed to be well. No more drips. Until today. The lady of the
house had a big shower (why does it take so long to wash hair?) and
there's a proper little stream coming down into the kitchen. It seems
to be coming from the same place, but my new grouting and sealing looks
fine. The adjacent bit of wall is not pristine, there are hairline
cracks in some of the grouting, but it doesn't look bad enough to allow
that much water through.

So how invisible can a gap be and still let water out? I really don't
want to re-grout the whole damn thing. Also, and tips for pinpointing
the leak would be appreciated (I'm thinking fluorescent dye or
something).

TIA


John