My window sills are rotting. I think it's called the sill - it's the bottom part. It appears to be a 2x8 type board on a slight outward/down angle. It extends left and right slightly beyond the window frame on the sides.
Some of them in my home are fine. Others are like sponges - I can stick my finger into them an inch or more in a few places. The remaining window parts seem fine.
Is this a DIY job? I'm comfortable with this kind of work. Someone told me "yeah, pull it out, slide in a new one, paint, seal, and secure it and you're done".
When I look at it, I don't see any good way to remove it.
Use a sazall and cut the sill into tree pieces. The center piece will remove easily and allow you to try out the piece on either side. Cut off or pull nails. Cut new sill to fit slide into place, nail and caulk.