Is it rot or just delaminated? If it is just delaminated. I have used a cure that a chemist friend came up with, that is, two part five minute epoxy mixed with denatured alcohol. The mixture is very thin and watery, It soaks into the wood, then the alcohol evaporates, then the epoxy goes off. Next day, sand and finish.
The result is great.
If it is dry rot, you should use "Get Rot" or replace the bad area. Dry rot will keep on spreading.