Call me crazy, but I'd just remove the airbag light from the instrument cluster and be done with it. If you know the airbags are working, why go to the expense of replacing a bunch of parts to turn off a 50 cent bulb?
This sounds a lot like deja vu....the exact same thing happened to me about 4-5 months ago...first it was the seatbelt ....then they replaced it...then the light came on again...which was because of the o2 sensor...