Learned a lesson and want to share.
Purchased a '08 CLS550 CPO in Jan (2010). Upon purchase attempted to call in & activate Sirus Sat Radio subscription. The head unit would not activate, following numerous calls to Sirius, they referred me back to my dealer.
Dealer was friendly, accepted the service repair fix request, ended up chaning the comms module (mounted in trunk) afterwhich the Sirius would still not activate. Called them again and again and "Finally" got a Serious Sirius Tech on the phone wherein he advised that the module installed by my dealer (OE replacement for the 2008 CLS550, i.e. same part) is not capable of receiving the "Best of Sirius/XM Everything" service (subscription) package and can only accept the "basic Sirius" sub pkg. Once we downgraded the subscription the radio activated as its supposed to and the sat radio works fine.
Lesson Learned - if you purchase a CLS550 (at least as 2008 model), you cannot subscribe to the Best of Siruiis/XM Everything pkg and can only activate your sat radio using the Sirius basic pkg.