Patch the joints with window glazer's putty, prime with Kilz II.
However, if the house has lead based paint on it, about five years is all you will get out of a paint job. Painting every five years is a real pain in the neck, even though you do have the best type of wood siding. I painted my redwood several times with great care and preperation but the lead paint underneath turns loose, blisters and peels every time.
It is time to cover it with vinyl siding for a maintenance free home.