From the photo showing the leak it looks like you MIGHT have water seeping out from under the glazing bead, heres an explanation how with some pics....
The rubber gasket outside where the glass sits against is not as waterproof as you might think - its ok but its not 100%, looking at your internal picture that tells me the pvc system is 'Duraflex' and if my memory serves me correctly Duraflex use a Q-Lon gasket outside. The problem with rubber and the Q-Lon gaskets is they don't fuse together very well when the pvc sections themselves are welded during manufacture, this is the weak point in the seal, yours more so because of the way the frame is sitting and is acting like a cup allowing water to gradually seep past the gasket, shock horror you might think.......well no, window systems have an in built drainage system to allow for this minute amount of water to drain away.
The picture below shows the glass removed and a slot routered/drilled into the frame, this allows any water that seeps past the gasket outside to drain into the hollow chambered pvc section, the second picture shows what you have which is a 'face drain slot' which allows water to drain out, the cap is there just to cover/tidy the drilled slot up (why it was fitted upside down is beyond me), just un clip it and push it on the right way round.
In some circumstances the slot inside under the glass is not drilled, rushed manufacture is usually the cause and this allows water to build rather than drain away, eventually it has nowhere to go other than to seep through the internal glazing beads, the water WILL at the same time as this be touching the underneath of the glass unit, once it does this it is only a matter of time before the double glazed unit fails, if its been like this for a year then i suspect it hasn't got much longer to go before it steams up.
What needs to be done now by the site manager is to send their glaziers/window fitters back to remove the glass to check for this internal slot and drill one if its not there, also a quick water test needs to be done to see if its draining away outside.
The rubber gasket outside where the glass sits against is not as waterproof as you might think - its ok but its not 100%, looking at your internal picture that tells me the pvc system is 'Duraflex' and if my memory serves me correctly Duraflex use a Q-Lon gasket outside. The problem with rubber and the Q-Lon gaskets is they don't fuse together very well when the pvc sections themselves are welded during manufacture, this is the weak point in the seal, yours more so because of the way the frame is sitting and is acting like a cup allowing water to gradually seep past the gasket, shock horror you might think.......well no, window systems have an in built drainage system to allow for this minute amount of water to drain away.
The picture below shows the glass removed and a slot routered/drilled into the frame, this allows any water that seeps past the gasket outside to drain into the hollow chambered pvc section, the second picture shows what you have which is a 'face drain slot' which allows water to drain out, the cap is there just to cover/tidy the drilled slot up (why it was fitted upside down is beyond me), just un clip it and push it on the right way round.
In some circumstances the slot inside under the glass is not drilled, rushed manufacture is usually the cause and this allows water to build rather than drain away, eventually it has nowhere to go other than to seep through the internal glazing beads, the water WILL at the same time as this be touching the underneath of the glass unit, once it does this it is only a matter of time before the double glazed unit fails, if its been like this for a year then i suspect it hasn't got much longer to go before it steams up.
What needs to be done now by the site manager is to send their glaziers/window fitters back to remove the glass to check for this internal slot and drill one if its not there, also a quick water test needs to be done to see if its draining away outside.
