Upgrade R8 cruise control

Hello together. Has anyone ever retrofitted a cruise control from you? I bought a retrofit kit of, I might mention later, bought, after check my chassis number on the part of the seller my R should already have the necessary cable set on board, so only the switch block and the lower steering wheel cover would have to be mounted, I also got an illustrated guide, so far as good. The whole then still encode and finished. Now it is unfortunately so that every W and even the Audi centers around me refuse to retrofit, since no one wants to assume responsibility, should make a mistake. And they unfortunately find no information about the cable set already installed, why can the Audi people not do what an online parts dealer can? O-Sound: “With a golf or polo it’s just going, with such a rocket it looks different”. You don’t want to intervene in the speed control afterwards and Audi allows I’d like to go to Austria and Italy soon and I would like to have the part on board, we know how quickly the allowed 130 will be flown through. The seller refuses to take back the stuff if all the ropes are tearing, because at least the call period has already expired. I think I can get it in case of an emergency with the liability for defects on the wrap. I would much rather have the part naturally in the car. I would have imagined it to be easier. I’ll tell you more.