Not being funny Clear Vision but the concrete lintle looks wet,probobly not the problem but it does look like your going quiet high with the water.
This is your problem, my friend.
Suggestion: Now that you have clean tops of frames, just keep them clean periodically, say every 3 months or so.
Keep your brush & water away from that lintel, just wash from the top beading down.
If you are going to wash the top frame, one quick wipe wipe with a scrim before you do the rest of the window.
Let the client know that periodically you will wash the top frame thoroughly which will cause a little spotting.
Oh, and the side frames are quite thin too, so just keep off the frame as much as poss on this one, that's all you can do.
Luvvly jubbly
