I just undid the pipes and let it piss out into the atmosphere. I know it's a bit naughty but in the scheme of things one more car leaking its AC gas isn't going to hurt. Loads of Supras have already leaked their gas out through old age.
Nah, it was a white one.
Anyway I'm there now. The matrix is out and I've found the leak. It's a tiny pinhole, too small to see by eye but pressurising the matrix while submerged in a sinkful of water showed its location easy enough.
I called the local Serck's and they can fit a brand new core to it for £68 if I take it down there tomorrow.
I'm not looking forward to putting it all back together though!