Great video on how to fix a bunch of zipper issues. Handy to have on hand for harness, rucksack, and concertina bag zipper problems. Implemented one of the fixes in the video (took less than a minute) and that fix is still going strong after a year.
I had a concertina bag whose zipper stopped working one day. Tried out the fix in this video which only took a few seconds, and that concertina bag has kept on ticking for the past 2 years without issue.