There is nothing on a P38 that can't be mended in one way or another but you do need some instruction and there's a lot of it about. You may have heard of RAVE which was the Land Rover workshop manual but it hasn't been updated since 2005. But, as the P38 ceased production in 2002, who cares.
RAVE can be downloaded from https://rangerovers.pub/downloads/rave.zip but it might take a while as it's a pretty big file. To run it, simply double click the rave-lr.pdf file and you're in.
There's also an online version that can be found at http://workshop-manuals.com/landrover/p38/range_rover_workshop_manual_volume_1/
The full parts manual can be found at http://new.lrcat.com/
and if you can't figure out exactly what the problem is, there's quite a few decent guides to the common faults that can be found at http://www.rangerovers.net/newrremedies.html although it is a little out of date now with some of the advice as it hasn't been updated since the original site was taken over by a Canadian company who allow it to be run by the main reason this forum has been created.
There's also a few archived articles of use that SpiggyTopes (Peter) has uploaded to Google drive that can be found here https://drive.google.com/folderview?id=0B4azhgT5UI-QWW9TQlhUWE9FWUE&usp=sharing
Having also got fed up with some interfering, self centred, redneck moderator with nothing better to do, I'm on here as well. Richard Gilbert although known at work as Dick (hence Gilbertd), I've currently got an ex-police (so with a very odd spec) R reg (98 model but built in October 97) 4.0 P38 on LPG and have no intention of selling it ever. Currently showing 307,000 miles, but with a nice new engine from V8 Developments (highly recommended) 20,000 miles ago. Just got to keep replacing the other bits that are wearing out. Also got a 97 4.0SE that I bought with the intention of sorting the odd little problems and flogging it on for a profit. But like all great plans, the thing had been so neglected that as fast as I sorted one problem, two more appeared so it's currently getting the better bits swapped onto the ex-plod before it goes to a local Indie who breaks them for spares. Oh yes, and I previously had a 93 Classic LSE, also on LPG, so know a bit about them too.