Ever had this problem? We have a shower cubicle in the bathroom which with three females in the house gets contant use. Over a fifteen year period we have had to have the tray replaced three times because of leaks into the kitchen below. Twice this has also necessitated a new kitchen ceiling (oh! the mess!).
In desparation on the last occasion when the leak started again before I had even had time to redecorate I inserted a large inspection hatch which pivots down and allows me to get at the waste oulet and relace/retighten as needed before it all gets out of control. I would also add that the shower trays have been fitted by reputable plumbers who tell me that this is not an uncommon problem. The Force 4 Hatch was easy to fit and is barely noticeable.

I find Sikaflex the ideal bathtub sealant, ever since I did it (six years ago) I've never had to revisit it, whereas the uselesss stuff the plumbers merchants sell only lasted a few weeks and went mouldy!

Thank you David. Good tip. I used Plumbers Mait (sic) around the wastetrap from where the leak was coming which has worked so far. However, with my hatch it will be no problem to reseal with this next time.