Fuel Injector Pump on '72 220D: my problem?
 

My car has been slowing down. I thought it was my fuel filters. I changed them but it seemed to make the car more sluggish. Before changing the filters I could get up a hill with a top speed of 23 mph. Afterward, I couldn't reach THAT speed and it was running rough, too. There is a big airbubble in the prefilter - after I pumped the fuel with the screw on top of large filter opened.
Could there be more air in fuel system?

Reviewing the manuals, I saw the injector pump requires fluid, but, all I could find about the fluid was that "12" were required. 12 what? Pints, quarts? And what? regular motor oil? Any 1972 220D experience and wisdom on this matter?
Could the injector pump be the cause of it being sooooo slow? And how can I tell if the proper fluid level is there? And what is the proper fluid?

I appreciate and trust this forum and it's members more than anybody when it comes to our MBs.

On the top of the injection pomp there should be a screw off cap with OEL written on it. Use regular engine oil. IF you add too much it will run out of the overflow pipe. Start by adding 6-8 ounces.