After all CEN customer service is not that bad; they wrote:

"hhello Simone

sorry about your problems you have been having. i will send you out a clutch for your 3rd speed. also i will send you 3mm nuts for your shocks."

It seems there had been a mail server problem as the e-mail is dated two days ago.
Now I can say I'm satisfied by the level of service and I'll continue to trust in this company.

Simone