Yes, that is the oil about which I first learned about the corrosive properties of excessive ZDDP.
In the late '80s, when the current API spec was SG, the GT 50 was labeled SD, an obsolete spec. I asked our tech rep, a chemical engineer, did it not meet current specs? He said it did, but it wasn't intended or desirable to be used in passenger cars because the high level of ZDDP was known to be corrosive in some situations. So, by labeling it racing only, not for passenger car use, and using an obsolete spec, it protected the company in the event of damage due to a misapplication.
Several years later, the racing oils were updated with the then current spec, reversing the policy. I think they were still labeled racing only. I didn't keep any of the documentation I had that would nail down the timeline because it was just old news. This was all before the ZDDP reductions started. Having the labeling and a date code would give me a reference point of a before or after date and help satisfy my curiosity. Sometimes the date code was on the box. OC23D translates to Oil City, March 23 1994 package date. Later codes were longer. Thanks.
