I had code 19 flashing at me shortly after I bought my S type. Its definitely airbag/clock spring related as you say. Bet my seller thought there was a serious problem and wanted to part with it, but in reality i just took the clock spring out and cleaned all contacts with wd40 - no issues for 18 months now! As Lazlo said, I would check every single connection point and clean them up. Its a common area for dirty connections.
Dan