This won’t be a great deal of help but I used a colourless fungicide/preservative (name I don’t remember) that I was recommended by our local saw mill. It goes on quickly and soaks into the wood to preserve it rather than seal it like a varnish/paint.
Pros – zero flaking and retains the natural colours of the wood.
Cons – difficult to tell when the protective effects are lessening so I need to remember to re-apply it.
More cons – it goes on mammothly quickly – it is almost like water so it just splashes on and soaks in. I just resealed our shed on Sunday – gave it two coats and it took less than an hour.
If you are interested I will look up the name tonight.
I would have considered the Osmo stuff myself (I really like their stuff) but I couldn’t find a clear one and I really didn’t want to colour our wood.