Just yesterday I thought about it again when I heard a LC diesel, oldish but as quiet as you can get. My 4,2 diesel(140K km) is extremely noisy aswell. The book says to adjust or check the valve clearance every 20K km. This has been done by SAC Boksburg, but its still noisy. Only thing that I can now replace is the push rods, at R280 a pop, I need 12.
I dont know the 4,8 petrol, but at that mileage It doesn't sound right.
For my petrol vehicles, I use Castrol Edge 5W40. Fully synthetic. I was even contemplating to use it in the Diesel Trol. Maybe even the Edge Sport 10W60. IMHO that might be the very best oil money can buy.
Some other oil that might do the trick is this ultimate stuff from shell Helix, they used it in that Patrol Extreme challenge of some sorts. Google is your friend.
If I might add. Never cut back on oil costs. Give your Patrol the best.
'96 SGL-D PATROL (GQ)
'07 SUZUKI BOULEVARD 1800
'06 YAMAHA 700 RAPTOR