My son snapped one of these bolts when reinstalling the mount on his 300D. Still not sure why unless the bolt was in a terrible bind against the side of the mount. He ended up having to remove the arm from the side of the engine. There was just enough sticking out to back it out with a screwdriver. The passenger side mount is difficult to remove because it is under the turbo and a bracket that holds the air filter drain line. Good luck! I'm sure you'll get it.
1984 300D Euro