What's the firewall throttle bushing called, where do I get one?

My '81 300TD TurboDiesel wagon has some kind of throttle bushing (rubbery filled metalic thing that screws onto the firewall and holds the throttle linkage from firewall to the "stop engine" lever on valve cover) on the firewall that seems to be deteriorating and the acelerator is becoming very mushy. I'm sure I'm only getting about 1/3 of the actual throttle so I'd like to replace this. I don't know what to call it, let alone where to get it. If anyone has any knowledge as to what this is called, I'd appreciate it. Thanks so much!