LR Disco adjustment tappet screw continuance follow on from post 50209

Forumites,
Ok again this follow on is just a story about how things happen..... After the RAC truck had dropped the Disco off at home I found the broken tappet screw, I bought eight new ones and fitted them, as you would, wanting to "do the right thing".
All week everything fine, towards the end of Friday the old girl didn't seem to be performing as well as she should be. Not wanting to be alarmist I blamed everything except the vehicle, head wind, slight hill, carpet stuck under the pedal, you get the drift.
Come Sunday evening after I had dropped my daughter off on the way home all was not well. As I closed the gates the engine had again developed a slight missfire, and a faint sound of popping back through the inlet manifold, this time event wasn't as sudden and the popping noise wasn't as pronounced.
Here we go again.............. Ripped off the rocker cover and only now noticed that the adjustment screw on the number four valve was slightly lower than the other seven screws which would indicate that something was amiss. I removed the rocker shaft and found the ball on the adjustment screw on the number 4 valve worn away, plus I could now see the valve stem cap resting in one of the cavities in the cylinder head, luckily it hadn’t dropped through. I’m assuming what happened from her on in. Whilst I was putting the rocker shaft back after the adjustment screw snapped, the rocker shaft got caught on one of the pushrods, I’m not sure if this dislodged the valve stem cap or not. What ever happened, I didn’t notice that the adjustment screw on this valve was lower than the rest. Keen to finish the repairs and get back on the road I suspect. So in a matter of 500 klms the ball on the end of the adjustment screw was beaten to death, and so worn that the rocker didn’t have enough lift to open the exhaust valve.
I’ve checked things out now and I’m going to install a second hand overhauled rocker shaft, the original one was showing signs of wear and a couple of the rocker faces were pitted. When I get the new rocker shaft I’m hoping this is the end of it. One thing for sure I’ll be checking everything twice when putting things back together again.