The book is called "power hydraulic system", publication number was S 73, and it was published by Jaguar and given/sold to the dealership mechanics so that they could fix the 88 and 89 model year cars and their insane power hydraulic systems. As built, the car had ride levelling rear shocks that were powered by this system. The "power brake booster" is part of this system, and finally there is a pressure accumulator for the ABS that has a pressure switch and a charge switch of its own. So, there are 5 solonoids, that are somewhat electrically interlinked. There is a pump, and a accumulator ball, and the hydraulic booster. Plus there is the reservoir for the green mineral oil in the rt front of the engine bay They were notorious for leaking and are no longer available new. Your avarage mechanic is likely to rake you over the coals diagnosing this system, because they won't know any more about it than you do. You are going to need to find an independant shop that has technicians that lived through the XJ40 dark ages. They will still be familiar with the system, and can likely fix it without bankrupting you. Or, you can take the time and learn how to fix it your self. If I were you, I would take that approach. The S 73 book is great, and lays out testing procedures very clearly. I don't think you can buy this book new, but a lot of these Jag tecnician training books show up on ebay from time to time. If you like, I will ask around some of my old Jag buddies and see if anyone wants to get rid of one of theirs.