I was doing an Angel Flight to Pittsburgh in 2003 9/26/2003, and the return leg turned out to be a night flight in IMC over the mountains. As I was flying home alone and tired, challenged with turbulence and strobe reflections. I realized that my turn and bank coordinator was bobbing around like rowboat in rough seas, and would be difficult to use flying partial panel. My vacuum pump had 470 hours on it, and I realized that I had accepted too much risk. I have since turned down this particular flight, and am limiting my night IMC missions. I began looking for options to back up my vacuum pump.