My friend the tech where I bought my C240 was showing me some stuff in a small plastic bottle. It had an MB logo on it. The bottle looks sort of like a slightly overgrown superglue bottle.
He said that it is some sort of lubricant that he uses on interior squeeks and noises. He finds where the parts are rubbing together and puts this stuff between them. It can lubricate plastics, vinyls, rubber seals and the like. He said it stays there for a very long time.
It sounds like the trick will be finding where the two parts are that are rubbing together.
However, if it is a click, it may be something just loose.
I remember you mentioning this when we first got our cars. At that time, I actually pulled around on my console to see if anything sounded or felt loose. Mine just does not have this problem. If you pull and push can you feel anything loose?
Stay after the dealer. If you deal with them firmly but courteously, I'm sure they will fix it somehow.
'01 C Class, Six Speed
'84 Euro 240D, manual, 533K miles
'88 300E 5 Speed
'81 300D Daughter's Car
Over 800,000 miles in