If the valv. is not opening can you pop the cover off the servo and see if that is cycling, do you have power to the servo. as for spray if you don't have cab cleaner I have used brake cleaner but very small amounts i have also used wd-40 some thing that will burn off that you can tell if its sucking air just watch your amounts so you don't pop a cycl. But I'm still leaning toward a clutch issue somewhere. Did you by chance replace the bearing behind the speedo I had a friend replace his one time and the flanges was seated right and put a bind on everything soon as we straighten that out it was fine.