In article , Andrew Gabriel
writes

When the units are replaced, check and clean the drainage channels
under the units, so that water that inevitably gets into the frames
can drain out without collecting. A common reason for failure is
the units end up sitting in a pool of water in the frame which
isn't draining away, which damages the seals over time, and pretty
instantly if it freezes. They should be lifted clear of the water
drainage channel.

On wooden windows I've taken to back filling the gaps around the DG
units with neutral cure silicone. I thought the risk of trapped moisture
was too great so made it so it can't get to the unit seals.
--
fred
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