There is no simple answer to why there is damage to your window frames after only eight years. It is possible that the windows were not properly installed, weather conditions adversely affected them, or the windows themselves are not of high quality. There are two possible solutions to your problem. The longer and more laborious method is to first remove the existing molding where the glass and the frame meet and then remove the glass pane itself. After carefully cleaning the bottom of the wooden frame, apply a bed of silicone caulking. This will prevent any further damage to the window frame. The second possible solution is to remove just the molding from the outside of the window, clean it thoroughly and, after allowing it to dry completely, reseal it with silicone caulking. This works much better than simply caulking over the wood.