1991 Mercedes Benz 500sl Removing the right rear rotor

If you are speaking of the Torx set screw that holds the rotor to the hub, often times this gets seized due to rust. A trick to get this out is with some rust penatrent. If it still is stuck you may need an impact driver and a hammer to get it out fully. Also if you don't have a Torx bit to fit the screw, these can be purchased at auto parts stores.