The only time I'd worry about repairs to technical garments is if I needed it to be waterproof. I have replaced the zippers on goretex jackets myself - but this was in the days when they had waterproof flaps that went over zippers, so I wasn't worried about how waterproof my stitching would end up being. And given there was a flap, I sewed & reinforced the hell out of things to make sure it would be reinforced enough for what I needed because it's not like people were going to see it.

I wouldn't do that with the new waterproof zippers that don't need flaps.