Scott,
Repairing the clock is fairly simple. Remove instrument cluster. Remove tach&clock assembly. Gently pry clock hands off. Leave tach hand in place. When you get the clock works out you will see two electrolitic capacitors. One of them is probably bad, but go ahead and replace both of them. They cost $1.00/each at Radio Shack.The original ones are rated at 16 volts; the new ones at 35VDC. The size is 100uF. Radio shack part No.272-1028. I repaired the clock on my 1983 300SD last fall.Works fine. I also fixed the glow plug relay by replacing a capacitor. Same size as the one in the clock. Seems as though the 16 volt rating is not high enough. A fully charged battery at optimum temp. is 13.2 volts. Not a lot of leeway there.
Bill Lewallen Lexington,Ky. Where diesels purr and turbos whirr and our cars are full of the Green coolant.