You should not have to completely remove it but you will want to get it where you can move it back far enough to replace the flex disc. I am speaking from the way my E320 is built but I am thinking it should be the same way. Look in front of your center bearing for a big ol nut. Loosen it up and this will allow you to "compress" the drive shaft from the front flex disc toward the support bearing enough to replace the flex disc. Make SURE you mark the orientation of the drive shaft in relation to the position of the disc on the back of the tranny that the flex disc bolts to. You want to put everything back the same way. Also, the book recommends that you use new bolts/nuts when replacing the flex disc. Torque everything to spec.