Several years back, when a similar problem befell the back deck on the Rutland property, I conferred with my seemingly intelligent brother-in-law. His 'remedy'
was to cover the older boards with new boards going in the cross over direction and then he applied some sort of coating. Darned if I recall what it was; but, it stayed in good condition for a good dozen years, at which point I was ready to vacate and sell (or sell and vacate). It survived some brutal Vermont winter weather so I suppose he knew what he was doing.
The difficulty here is twofold:
1) I have no idea what he did beyond that cross over boarding (brain fry or old age? Not sure)
2) he is long deceased as he passed on a little more than a year after the job was done.
Last up, I advise against those indoor/outdoor carpety things. Mother had that on her outside terracing and it was beyond hideous- at least I thought so. She was of limited visual ability by then so it didn't macaw her in the least.
Sorry I can't be of more help (or maybe of any).