After the O2 sensor is changed out and the tuneup has been done. I did spark plugs, wires, dist and router. All that you mentioned has been done.
All the vacuum lines I could fine loose. Including taking off the air cleaner. After changing a few the ones leaking got louder.

I ran out of temp tag solutions so I went down and bought a quart of rubbing alcohol and dumped it into a quarter tank of gas. I drove at least 20 miles and sat in line for another 30 min. I passed with flying colors. Next year I will see if it is the fix or not. I only had two of the three failing when I went thru. I have what I did on my 89 300sel 194000 miles.