BMW approved upgrades are those from DINAN, ALPINA, SCHNITZER. however these are only approved in a way that each firm gives you equal warranty on on their own work. if you use a non approved upgrade such as blitzen shocks and installed them yourself and the mounts collaspsed due to poor work then BMW will NOT support you however if the engine blew then it would be covered. so just buy parts with a warranty if its really that important. But just like in Vegas sometimes you win sometimes you loose. (but you can switch the odds in your favor with planning and a heavy outlay)