I agree with what has been previously posted in the replies, but I would add that you should, make sure that the new screws are getting a good hold on the wood. If it is degraded enough, the wood will no longer hold on to the screws, and they will just turn uselessly. You would then have to drill out the rotten wood and dowel the hole. Couldn't you just curse people who use brass screws? Galvanised ones are another sin, as the galvanising doesn't last, and then you are left with a rusty steel screw.
Peter.