The real question is are you sure that the oil you used was Rotella T? I have been using Rotella T 15W40 at 3000 mile intervals for the last 15 years and it seems to be fine. I recently switched to Rotella T synthetic 5W40 because of better performance in the winter. At Wal Mart It sells for $12.84 a gallon which is the best price that I have seen for a diesel rated synthetic oil. I do not have enough scientific knowledge to know which synthetic oil is best but I am reasonably sure that It is better than any non synthetic oil. The one comment that I have is that you have to be careful when you buy it at Wal Mart. Both Rotella Ts have a screw cap with an aluminum seal as opposed to an external plastic seal like most other oils. The result is that it is not possible to tell if the container has been tampered with unless you unscrew the cap and check it before you buy it. So it is like buying eggs where you have to open the package to see if any of the eggs are broken. On numerous occasions I have noticed on a prepurchase inspection that the seal is broken on the synthetic oil. I have never seen a broken seal on the cheaper Rotella T...only on the more expensive synthetic stuff. I suspect that the employees are switching the contents with an inferior grade of oil. Its kinda like going to a liquor store and buying a bottle of Jack Daniel's that has been refilled with Ten High.
I know that I sound like some of a kook with a conspiracy theory but I worked for NCR for 23 years and I can tell you from real experience that many low paid employees in a retail store are about as honest as they have to be. I have reported it to store managers on 2 occasions only to be met with a blank stare.
I still use the Rotella T synthetic but what I have to do is buy it when i can find it in containers with the seals intact. The bottom line is that Shell Oil Co. needs to needs to rethink their packaging and come up with a container like the other brands have so that it is readily apparent if tampering has taken place.

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Tom Hughes
St. Louis
84 300SD
92 300D
86 300SDL