My 1982 240D will not start. Has #1 diesel in tank. Tried priming and even tried direct shot of starting fluid, which I realize is a no no, but wanted to eliminate lack of fuel as the issue.

It was running fine, although it has always been slow starting, required a lot of cranking. it sat for a few days and then would not start? Will it start if it has one or two bad glow plugs. The two easiest to access glow plugs were replaced in an effort to fix/determine the problem, and replacing them made no difference. Fuel feed lines and clamps were replaced fairly recently, I doubt if there are sir leaks.