who actually did replace them. The fact is they get older and they might not funtcion very well in case of the accident.
Mercedes has tested the first S classe Mercedes back in 1993 to test a 10+ year old airbag. Everything went oke, but they also say 10 years is a maximum life of an airbag. That usually means they are good for 15-18 years if not more then that. The first cars were the W126 series MB's in the early 80's so we haven't seen a car with 20+ year air bag.
1991-93 850i/Ci
850 driver side airbag : $762.50
850 pass. side airbag : $760.00

1994-1997
up to 9-94 driver side : $762.50
from 9-94 driver side : $690.00
passenger side : $760.00

unless you had the M-technik steering wheel (3-spoke) that one is also $762.50 for driver side

did you know that the 8 series starting from 3-94 (since the passenger side airbag) had a seat sensor in the passenger side ? so in case there isn't anyone sitting there the pass. side will not blow ? Most new cars has this feature since 1998 ! we had this all along ! I know because I had it replaced 3 weeks ago under warranty !
a $102.00 item but takes 4.5hours to gain access to the actual part ! so labor in this case is amuch more then parts !