I have a 1985 300 SD that I have been commuting with for a few months now. Yesterday morning I drove it to work, when leaving work I noticed the Glow Plug Light did not come on as it usually does. I also noticed a buzzing sound from the engine compartment. After turning the key (after the seatbelt alarm went off) the engine cranked but would not start. A friend had some starting fluid which we squirted very little into air intake. Tried a number of times to start it, with a few more small squirts we got it going. I drove it home (40 mi) and got it into my driveway. Turned the engine off, waited about 30 seconds and tried starting it again. It did start, and I am pretty sure I had that buzzing sound from the relay. This morning it would not start and after a quick inspection of the glow plug relay box, I noticed that the 80 amp fuse was a bit buckled. It has a hump in the metal, about 8 mm above it's original flatness... Any suggestions on what to check first?