One of my large upstairs vinyl window frames is leaking rainwater onto the window sill. The base of the frame is filling up with water, which is then overflowing onto the sill, where the window meets it. By comparison, the bottom of the adjacent window frame (which isn't leaking) does not have any water in it.
I don't know whether water is SUPPOSED to get in, but then drain out, or whether it shouldn't enter to begin with. Any suggestions greatly appreciated.