I took the gearbox into "the automatic gearbox company" in Rochdale on Tuesday. They have now stripped the box, and found that the bulk of the oil discolouration has come from the friction plates / clutch plates which all need replacing, together with the bearings and a few other bits and pieces.
They also want the torque converter to strip and inspect this, which is a bit of a pain because I thought that I had managed to avoid undoing all the bell housing bolts, hey ho, that's a few more hours on my back under the car, and a longer reinstall.
More money too.
I have completely stripped the FF box too, so pictures of this to follow tomorrow, I am just waiting for replacement bearings for this.