Got the part from this chap: https://www.ebay.co.uk/usr/robert8310
I don't know if he has any more for sale, but people could contact him. Kit No. was SP7761 (which is a Lucas No.).https://www.ebay.co.uk/itm/JAGUAR-XJ-19 ... 2749.l2648
Taken a look in the pedal box and foot well and haven't seen any obvious signs of leaking there, but will take a look at that I dare say when I get the M/C off.
Definitely losing DOT4, as I fill up the reservoir, pump the brakes (pedal goes to the floor) a few times and I notice the level is lower. Just need to find the puddle!
Yup, it's the process of elimination, all the fun stuff! I'll use this as an opportunity to go over most of the brake system and get it operating nicely.