During my research someone posted an interesting observation, They commented about bits of the coupler contaminating the sc oil. If you have ever changed the sc oil after 50,000 miles, you will have noticed the old oil is discolored and it stinks big time. I believe this is evidence of contamination and possible chemical breakdown. Also remember you don't have a filter to remove contamination like you do with your engine oil. I believe you are better off in the long run changing your sc oil every 30,000 miles as a maximum interval. As far as oil goes in general, over the years they have improved the quality. In 1997 when this model/ series of regal came out a common rating on motor oil was probably SE or SF, now it is SM. How long has GM sc oil been on the market? Has the formulation changed? I think with the right mix of turbine oil and amsoil gear oil, you could have something superior to the original formulation of GM sc oil, at least for a high mileage car.