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Rain coming in from the outside - help - new putty for window

I have got one large window which is a concertina window with four panes. The water is coming in through the putty and will eventually rot the timber on the inside. I keep wiping up the water that comes through on a wet stormy day when the wind blows the wrong way but ultimately the putty (or whatever it is) needs to be replaced as it is falling out and the water is seeping in on the inside . I am looking for a good tradesman that can replace the putty/or a window/glass filler in these 4 panels so that the water doesn't come in and it can look tidy once again and most importantly waterproof.