83 300D won't crank.

Hey, i've got an 83 300D Turbo that's causing all sorts of havoc for me. First the car would hold a charge for about two weeks, then there would be a voltage drop on startup, then kaput, no starting. I replaced the battery and everything was fine for a bit, then it began to happen again. I let my mechanic take a look and he narrowed it down to and replaced the voltage regulator(Tuesday), which was reading incorrectly before it was replaced and correctly after it was replaced. Wednesday evening I stopped by to pay him for the tow truck and on trying to start it to leave the mechanic it wouldn't crank. This was accompanied by a buzzing from the glow plug relay so we replaced that, assuming that it was dead, indeed it was, and was burned inside as well, it looked like something blew and blew big time. Then about an hour ago, getting in the car at home to go to a cousins birthday party it was dead again. Any help would be appreciated, these Tow trucks do get expensive after a while. I drove the car my normal distance each time in between problems (about 25 miles)