Another test (and I have seen this done at several sail lofts in St Petersburg, FL, including the OEM for my '85 H22 sail) is to fold the sail cloth, anywhere, and see if you can rip the cloth across the fold. If you can its time for a new sail.
I agree with those above, that if the problem is only with the leech, a loft will fix it. Some rips and tears can be repaired with sail tape, but that is only a temp solution, meant to help you get back, not a permanent fix. I have repaired several Hobie sails, by going do a local loft, and asking for scraps, and stitched two rows of zigzag around the patchs on both sides of the sail over the tear, but those were on good sails, and relatively short rips, 2' or less. I also put as short of of a zig zag stitch perpendicular about an inch past the end of the tear. Just to help keep it from tearing any further.