There was a factory recall on some later W124 driver airbags-something to do with contact corrosion in high humidity environments. Maybe you have one of those? When my one was replaced the new one had a silver metallic finish to the centre 3 pointed star emblem on the airbag whereas the old one was black just like the rest of the airbag. Your MB dealer should change it FOC by chassis no if it is this fault. Maybe worth checking out??