Restoring Larch wood cladding

[T5GRF]

Our garden room is 3 years old and despite two coats of OSMO when new the Siberian larch cladding is starting to go grey/black in places as the OSMO has failed.
Is it simply a case of sanding back the areas and reapplying a coating to protect? This would take some time to do as the building is 12 meters long. I was wondering if the areas could be cleaned up with sand or dry ice blasting to make the job easier?
I know there are wood reviver products but the building is surrounded by composite decking and has aluminium windows both of which could potentially be damaged by the acid used in these products.
Any other advice welcome.

[Snow and Rocks]

Is the idea of choosing a durable wood like larch not usually that it's allowed to grey naturally?

I suspect trying to maintain the "new" colour is going to be a pretty labour intensive/unrealistic task. A fresh coat of oil will bring some colour back but don't expect miracles.

[T5GRF]

We like the colour and appearance of the wood cladding when not ‘weathered’ I’m quite happy to look after it hence coating it with OSMO when new, I just don’t fancy spending days sanding back the weathered areas if there’s an easier way such as ice or sand blasting.

[Simpo Two]

I think sandblasting wood would leave ridges as it's not all the same density.

A sander is probably best, finish with a coating of your choice, and then apply subsequent coats of finish before the surface deteriorates again. Unfortunately you're fighting nature.

[OutInTheShed]

The grey won't just be on the surface.
If you don't like the grey, you might have to use a preservative with a strong dye in it.