Hmmm.... I'm a bit stumped.... If the motor is running nicely, and a litre of oil usage over 6000Km, I believe is fine. Here is another train of thought...... Being a new rebuild engine, you may have driven it gently ( running in ), which is why there are many different views on "running an engine in".
I do a LOT of stop start short trips with my Patrol. I work 7Km from home, and have had similar white smoke issues from time to time, so here is my train of thought and I do find that this works for me. My motor has done about 70 000Km since I did my rebuild and all is well with my motor.
With Alfin pistons and rings you need compression to press the ring up against the side of the sleeve to get a good seal. There is a cross pattern on the sleeves when they are, I presume honed to create and hold a type of oil film over the entire sleeve, so as the piston ring slides up and down there is always a thin film of oil between the two. If the compression is low, by not putting your foot down on the accelerator and pushing the revs to the 3000rpm mark under load, the Alfin piston ring is designed to push out and up against the sleeve. More compression will make the ring push out more, and less compression = less pressure on the sleeve.
Where am I going with this??.... Maybe the sleeves, or bores have become slightly glazed. I think a slight glazing of the sleeves can be burnt out with a good aggressive long ( more than 80Km )drive. On start up, DON'T let it idle !!!. When you pull away do an aggressive pull away..... don't wheelspin obviously, but don't pull away like driving Miss Daisy, do a good average to just above average pull away. Keep the max revs to MAX 1500 rpm ( The motor is still COLD ). Don't be scared if you see HUGE plumes of black and/or white smoke coming out your rear.... again I mean your Patrol...

...... so you want to get short crisp quick gear changes with rpms at 1000- 1300 rpm put your foot flat on the accelerator ( obviously if safe to do so ). You want to push the motor to get the biggest explosion at the lowest rpm while cold.
The temps will rise to normal operating temps quite quickly. Now don't baby the motor.... this TD42 is a BIG donkey and an handle punishment better than you think, so put your foot down and push the motor a bit. That motor is more than ready to take a bit of hard work.
Get the EGT's up into the 550 deg C mark ( pre turbo) and let it stay there for a short period of time UNDER LOAD!!. 550 deg C is still well under critical temps of 700 deg C. When you are returning home don't let the engine idle for 2-3 minutes, but rather slack off the power to allow the oil to cool down via the oil cooling system you already have. If you stop at a robot, and pull away ...... floor it to 2000rpm and change gear and repeat till 60Km/h is achieved then hold it there. Do this at every pull away.
Your EGT's will not shoot up high doing this and your oil temp will also not go up too high. When you are at home the turbo will be spinning at a reasonable rpm and oil temps will be acceptable. Idle for about 20 - 30 seconds MAX and switch off. next day start up and repeat process.
Check if on day 2 there is an improvement, and if there is a difference on day 3 after the second hard drive. If you decide to do this, let us know the results.
You can ease "this style" of driving up a bit but continue to drive this way on start up. Don't punish the motor when cold, but don't baby it either, you need those Alfin rings to do what they were designed to do. You will have to assess how to drive the Patrol under whatever the weather conditions are. What I'm saying is if its snowing let it idle for 30 odd seconds before driving away, if you are in the Namib desert drive it almost immediately after start up.
Please note that this is only my opinion, and it is working for me..... this is your decision if you do try this, as I assume there will be differences in opinion on this matter with other Patrollers and enthusiasts.