@Rox, Goodness me, I have also the exact same vehicle, but a facelifted version, I am also starting to experience the same issues as you now with the Auto-hold function, the brakes stick on and as soon as you let go it sometimes either takes time to let go or it gives that kind of a launch control, very dangerous so I just turn it off! Useless piece of kit. See this is my first MB vehicle, and I also thought the same, why should timing belts need changing at 20K!
Thank goodness you’ve got rid of it! Now I am glad this lease is coming to an end, wish there was a way to complain about the overall vehicle experience but like you said, must be very careful as they can blame anything on us. Thanks for the advice!