Y62 dust in engine

I have a Y62 Series 1 which has done a fair amount of off-road driving - not mountain climbing, more touring on the Tanami, Gibb River Road, etc. Bought from Nissan new in 2014, done 170,000kms and serviced 16 times by Nissan as per the 10,000 service schedule. Started a small whine about 3 months ago which has now been diagnosed as dust in the engine, 3 cylinders already badly damaged, and described in my last Nissan service report as “this car needs a new engine”.
Has anyone experienced anything similar.

Has there been a break in the inlet piping or has a vacuum hose been left off? Did a service mechanic not refit the air filter properly. Do you run a snorkel?

Nissan can’t find any damage, and can’t explain what went wrong - that’s after inspecting the car for a week. No snorkel (none available in 2014 when I bought it) but there has never been a build up of dust on the filter. There is a fine layer of dust in the filter box on the engine side.

I can only think that the filter wasn't fitted properly and it was never noticed. Did it ever backfire at any stage? i have had experience of the filter housing on a Falcon popping open, after a backfire.

Never had any backfires. I can only think the Nissan filter doesn’t handle bull dust very well.

The service intervals are reduced for dusty driving.

The vehicle was serviced immediately before and after every trip - for one trip it was serviced half way

I am out of ideas, sorry.

I've seen this on a fb page,to be honest I've never seen or heard of it happening before either,

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I have just had an official response from Nissan Australia.
“The dust has gotten past the air filter and through to the engine. The engine bay showed signs of severe off-road driving conditions and was covered in dust. The case of the concern has been deemed as environmental due driving conditions”.
The current dust in the engine bay came from a trip to Arkaroola in May, about 300kms on a well graded road. But Nissan is saying their car is not designed for Australian outback conditions.