It's because the plastic pipes have gone brittle.
With the aid of a pick, I managed to clear out the broken/brittle crap inside the T-Piece and then chop them back and force them back into the T piece as a short term fix, but that won't last.
I don't want to cobble together a repair with some generic hose that won't look right, they're easy enough to replace and not horrendous money (especially if buying the pattern part for half the price - though I wouldn't do that):
https://maltings4x4store.co.uk/inlet-ma ... C_-SsehmCy
But it seems to me this must be a common problem and they will go again?
Does anyone know if there's an 'upgrade'/mod available for them?
I have done a quick search around on the internet (I assumed someone in the Land Rover/Jaguar community would have done something by now) but haven't spotted anything just yet.