i just bought a 99 CTD with 75K on it. i sent in an oil sample to a local analisy and should be geting the results back tomaro, what things should i keep my eye out for that could give me an indication of what condition the engine might be in. also when i drained the oil from the engine there were yellow bubbles in it. any ideas on what this might be. Cummins west said that some delerships put a die in the oil that gloes in black light to check for leaks. but i place a sample of the oil under a black light and nothing.