The joint is not rubber. It is two U shaped pieces of metal. On one of those there are two small black looking rubber bands. I guess they would stop metal to metal contact. Yet if they rot and fall off they present too much slop in the system.

Just follow the linkage along and you should find it. I still have that car but it is not available to me right now. Also it was many years ago I dealt with that.

I have to assume but may be wrong that all the 83 240d throttle linkages where the same. The only thing that may or may not make a difference was my car was a stick shift. Why I specifically mentioned it is if those black rubber or plastic inserts have rotted off. I do not think the linkage will operate quite right if an attempt is made to compensate for them missing.

The part I am mentioning is also out in the open. Not obscured by something else.

In a way the simplest test is again to have someone put the pedal to the floor. While you make sure the lever on the injection pump is going to full. With the rubbers gone I do not think it is possible.

If someone before you tried to adjust the linkage with the rubbers missing. I am not sure what the effect would be.