We recently moved into a house that took a lot of shortcuts. The exterior window casing was not thought out well. Mostly the bottom window sill piece is completely flat and has no slope, so water can't run off, and water collects on the sill. Some of the wood on the side piece of casing has a spot that's rotted out. My question is how can I replace the bottom piece with a sloped piece, or how can I add a slope? The ideas I have so far are cutting a slope into the existing piece in place with a blade saw of some sort, or cutting out the whole bottom piece and replacing it with a new one that's sloped (could cut it after it's out maybe). It's a nice piece of treated wood, just needs some work.. any ideas or thoughts are very welcome!