I'm looking into doing this myself since my '06 Limited Coup is near the recommended 80k mi change point and is already leaking trans fluid and experiencing some shifting issues. The service manual says to use Shell 3403 ATF (MB 236.10) or equivalent. The driver's manual says to use only ATF approved to MB 236.10, MB 236.12. Synthetic Dextron III ATF may be substituted. If you locate the fluid fill tube just behind the engine cover, the fill tube cap has a little black plastic locking locking pin. If that has been broken then at least someone may have removed the cap for adding fluid. Not changing any fluid in your car when recommended or later I think would be a poor choice. in this case, however, the manual says that you never have to replace the fluid after it is replaced at 80K mi.