I just bought an 84 300d and the stuff you did sounds like a good start. One thing more would be to replace the shocks with blistiens or Boge shocks. I did it to mine and it drives so flat it is wonderful, no pitching or diving. Cleaning out the radiator with a washer was a great thing to do. Pull of the battery and bracket and look for any corrosion as this will lead to leaks in the cabin. I replaced my glow plugs and injectors. I live in chicago and live in an apartment. I dont like having to repair any thing in the winter as i am outside doing it. How old is the battery, if it is over four years old i would get a new one, i bought an interstate.

enjoy the car

bob