Mystery solved.

Phil, you're correct, there is a reinforcing ferrule in the tank outlet spigot, but much smaller. Its still there.

This comes out of the hose branch that goes up to and underneath the AC compressor, onto a steel pipe...You know, the one you cant see or get at with normal fingers...

The hose that goes up to the plastic tank has one as well, still firmly in place and I can't shift it. Have no idea how this one grew legs and wandered out.

On the easy bit now, just re-building, shaping, putting it all back together etc.

Wearing a shirt/tie (Sunday...) under a grey dustcoat somehow made it easier to get off with dignity.... Reckon if I had a LR logo on said coat it would have been easier still...