i've had BOTH of mine go "south" on my 97 Tourer. the first one did so LONG ago. the outer cover that keeps water from coming in somehow broke...and was "floating in there". i'd go to insert the key, and it wouldn't let me. i sprayed some WD-40....kept playing with it...and eventually, got the broken outer cover piece out of the way. then, for a couple of months...it would work for a while...and then if i forgot to UNLOCK it before riding..and i rode...the vibration would make it "go south again"! Sometimes, it caused me quite the problem
eventually, the other side started acting up occationally too. I'm happy to report BOTH sides work 99% of the time now...and i can always get them to work eventually (though sometimes, the bag locks on the start of the ride...maybe not so later...then works again at the end of the ride...etc.) .For me, it was the WD-40...and some patience (at times)...jigglying the broken piece around. I still have all original locks...and they still work.........
of course, a good locksmith would be a good simple answer to the fix as already noted

Sherry once had Champion bags on a RoadStar. their locks were well known for malfunctioning ...OFTEN! hers malfunctioned one time...with her HELMET LOCKED INSIDE IT! She couldn't get it out...so...couldn't ride off (helmet law here in Bama). The guys from the local Honda shop were nice enough to bring her a helmet to her work...then she rode it the shop..and they "broke in". That lock, NEVER worked again. I hear in recent years Champion has gone to better locks?
Anyway, you might be able to get that lock working again with some patience....like i did...depending on what is wrong with it........... Neither of mine have that outer cover that slides over to keep water out working...but...i've never had issues with water in it or the lock going bad from mositure.... For me, the few times my lock doesn't work on one bag, i just lock the valuables up in the other bag...and put the not so valuable things in the bag with the temporarily defective locking bag.