Some double glazing spacers with thousands of holes, yesterday:
(I was told that not matter how good the build, damp air goes in and out through the corners and through those holes and eventually saturates the dessicant, which is contained inside the spacers)
I’m afraid you were told wrong. New double glazed units will be fully sealed. Like everything, this has a finite life. In the case of mine (I made around 6000 windows last year and had almost as much roofing glass) this takes at least 10 years. Anything under that and I replace foc. Uv light and water can increase the speed of breakdown, so best to stop that from getting to the bitumen used to seal them. Most of my units come from Pilkington in Derby, so will be pretty industry standard. Same applies whether Argon or Crypton filled and whatever solar control / low e coating is on the glass. The desiccant is to ensure that any trapped moisture when the units are sealed doesn’t cause condensation.
OP, replacement glass is best (easy with wooden windows) some companies will do what you’re suggesting, then spray an anti mist coating on the inside of the unit which prevents reoccurrence before plugging the holes. No idea how effective though!