Well in the broad light of day the fluid appears to be atf I've spilt... There's no sign of a leak from the fluid reservoir, nothing in the servo, nothing from the front callipers so I'm guessing it's the rear callipers. I've filled the reservoir to see if it goes down again but fluid was still at the same level after pumping it for a couple of minutes. Going to monitor it but I'm guessing this is likely to be a rear calliper job...
I do have a diff procured a while back with the intention of curing the wobble and the unstoppable dribble from the from of the diff extension. The callipers on there are meant to be good but I guess an inspection of that is probably the next step. I wonder how much it'd cost for someone to fit it for me? It's a big dirty job for me on the drive otherwise.
Rich.