hello tony. i have seen the results of people switching oils in engines and trannys that have lived a long happy life using asphaltic based oils. all of the circumstances involved a popular brand of synthetic oils. one was a poorly maintained but otherwise good running jeep straight six that came to me with 3 broken push rods and a clogged oil pump.[a real mess]. sludge was loosened up and floated around the lube system after the fillup of this synthetic lube.another was a 5 speed overdrive tranny that had about 80k on it and stiffened up and would not shift until the synthetic lube was drained and the regular 90w gear lube was reinstalled. now don't get the idea that i have a problem with these synthetics. they are the best you can use in a machine that doesn't have some sludge in it. i have been cautioned by older peers against using high detergent oils in engines that were sludged up.good luck.

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