Off grid house build Orkney

Thank you, you have no idea how useful this information and this drawing is

Google "aluclad window profiles drainage system" brings up lots of different profiles, with quite a few rogue pvc/ aluminium frames, or inward opening. However they all need a working path for water to escape.

I tend not to work with timber frames very often, having found a niche repairing pvc. I've seen dozens with the drains choked with muck or swarf from the machining or covered by the glazing packers. A good handful have had drainage holes across the top of the window! Have a look along the bottom edge of a non leaky window, and try to identify any drain slots. Then compare to the leaky window bottom and top.

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There’s still moisture sitting within the frames weeks after that storm so there must be some issue with the drainage channels. The frames are engineered wood so unsure what impact sitting water will have on them. The resolution they recommended was different tape, another seal and silicone in a few spots.
The joiners both don’t think this would work and said taking apart each frame to do this will take some time and cost a fair bit in their time.

Thicker tape and a dot of silicone in the corners of the glass, may reduce water ingress into the frame, but it won't stop it entirely. Your DGU will still be sat in a pool of water at some point unless an effective outlet is created.

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I’ve put this back to the window company and asked how the warranty would be impacted if people have opened and modified the frames too and whether they would be happy receiving the invoice for the joiner’s time. I’ve asked them just to send up someone from their glazing team to come up and assess and am just waiting to hear back now.

Unless the joiners have installed the window upside down, or removed the aluclad facing and fitted it upside down, it's not really their job. Unless a customer doesn't want to deal with the supplier anymore, I wouldn't get involved modifying their window if there's still a warranty.