I have a 98 V8 Disco that lost 4th gear after a transmission service. It stopped changing up from 3rd to 4th after an oil change. The problem still existed after replacing the transmission, and then again after replacing the valve head. So that is two transmissions and 3 valve heads, but still not changing up to 4th gear. (And not the kick down cable out of adjustment - was the first thing checked). Then discovered that the selector lever was being held out of position by the selector cable being wrongly adjusted, pushing the selector lever on the side of the box about 3mm too far forward.. Adjusted the cable and problem has gone away - changes correctly again, and has done so for 3000 km of mixed driving. My hypothesis is that when the selector was in "D" the master valve was too far enough forward to allow full oil flow to the clutches that select 4th gear, but the tranny service business says this is impossible. I have tried to find a diagram showing the multiple oil channels and valves in the valve head to see if my hypothesis could be correct, but not been able to find. The photo is looking vertical with the front of the vehicle towards the bottom of the photo, and selector in 1st Any thoughts please?