I have 1998 E320 and when I accelerate then release the pedal I can hear a "clink" sound behind me. I check on the web and it says it might be the flex disc coupling.

Several questions need to ask?

Is it the flex disc or other?
What happen if I don't replace the flex disc?
Is it easy to replace flex disc?
Is it expensive to let someone do it, how much would it cost?