James I'm sorry for not explaining this better, but let me try here .

the Wavetrac is the carrier in the differential , all the axles fit into the diff N/A or srt the 2004 to 2009,,the 04 crossfire has axles stubs,,( this is where things change) the axle stubs from a crossfire or slk have to be sent along with your differential to Unitrax - call Rob at needswings ( he is the wavetrac dealer he will tell you what and where to send your diff,, they will modify your axles so that it pushing in and out of the diff ,they will return your C-clips and your diff with the axle stubs in it ,you may pull the stubs without removing the rear cover, to install into car,or leave them there.
now for the c-clip,,it is used in the 2004 Crossfire and slk 32 Mercedes when unitrax through needswings gets you diff and stubs they machine about .020 out of the grove on the end of the axle so a spring clip will alow the axle to be a push in type like the other Crossfires are now. if you ever decide to remove the Wavetrac to sell it or what ever, you should swap the axle stubs with whomever you sell it to if they have a SLK or an 2004 Crossfire this way they can install and drive and so can you. jim