Land Rover Repair: 2000 DISCOVERY SERIES II, lucas oil additive, discovery series ii

Question
I am trying to figure out this tappity tap tapp coming from under the righthand valve cover. I just changed the oil and used 15-40 and the thick Lucas oil additive - the noise is a tiny bit quieter but still it taps - at some rpm's it seems to go away. I  think its a lifter - what do you think? What can happen if I don't correct it?

Answer
2000 Rover V8 motors are know for developing noise from the rocker shafts.  The cure is two new shafts assemblies.  The lifters themselves are probably fine.

If you leave it nothing bad will happen but it may get louder.  Repair is not hard, though, so I'd imagine you'd want to fix it.