I have a '85 300 D, and I'm getting air in the fuel line. I have pressurized both the fuel and return lines, no leaks. I disconnected both lines before the fuel pump and put them in a jar of fuel. I then started the car, it is still drawing air. I also replaced the fuel pump and the fuel primer pump, no difference. Some suggested it may be the fuel delivery valve smash washer and/or o-ring. If that sounds possible, where is it located and where can I purchase them ?