sometimes, the carrier (which is rubber biscuit mounted) is just a little out of whack...or the magazine is off spec. combination of both may require that you flick the magazine with one finger, while pressing the EJECT button with the other.
MB owners are aware that certain changer models can be real pain in the rear as their design sux. they're unreliable, prone to failure, a cash cow for MB changer repair people, and prompts error msgs on the head unit display.
more the reason to figure out how best to append to the sound system, an MP3, Ipod type player.
I minimize my use of the CD changer (knowing full well it's a ticking bomb) and use the in-panel Audio 10 single slot CD player....which retains the factory issued look.