To prevent future log damage remove the existing sealer off the logs by corn blasting, install impel rods in areas where rot is starting, apply borate into the logs, chink and caulk all seams to prevent water damage and apply a breathable sealer.
Remember that rot spreads like a cancer. If one log is rotten and you ignore it other logs around that log will eventually become rotten as well. The cheapest way to handle rotten logs is to fix them right away and maintain your home properly.