VKB-SIM

Firstly, I would need the right half of the handle for my MCG Ultimate. The rubber is coming loose and some of the paint is gone.
The other case concerns a colleague with his MCG Pro. But that shouldn't make any difference in this case. Button 12 on this switch no longer reacts. So there is also no reaction in the firmware test window.
I would be happy to receive feedback on what I need to do for this. I also can't manage to insert one or more pictures here....

You need to contact the dealer first.
Regarding the Ultimate grip, there is a bunch of questions he will need to ask you before deciding what to do.
Same goes about the button.
We will try to help, but getting a ticket at the dealer's is an unavoidable first step.

Thank you very much for this “advance information”. Can you also tell me the email address that is ideal in this case?

Contacting your dealer is done through their website. When you log into your profile on flightsimcontrols.com, you should be able to create a ticket for the order with which you bought the grip.