ok, I know you mechanics out there are all very excited to find out what the problem with my wonderful '80 300 sd was. well, it was quite simple.
running on wvo with a broken thermostat (engine didn't get hot enough to burn every drop) and broken glowplug caused build up of black stuff in the precombustion chamber of cylinder #5, and hence bad combustion.
Incredibly good as I am I took out the #5 injector and heat shield, sprayed the chamber with carburetor cleaner and let it sit for a while. then I poked around in it some with a small screwdriver. then I started the car, without the last injector in it of course, and blew all the black crud out of it. I put it all back together and voila, problem solved. and yes I used a new heat shield. and no, I'm not worried about black crud particles in my 500k+ mile engine.

so please, don't be shy now, feel free to congratulate me with these accomplishments. and if anyone does decide to panic for any reason, remember to always panic with confidence!

please do not reply, it might make me think that people still watch this threat.