Removing the seat covers and replacing the pads is not a huge task; check the site for a description of the procedure.
Don't overlook the possible contribution of carpet to an odor problem.
'97 SL500, 40th anniversary edition
'04 Olds Bravada (SWMBO's)
'06 Lexus ES330
'89 560SL (sold)
SL--Anything else is just a Mercedes.
(Kudos to whoever said it first)