The Zinc wear addiative ZDP had to be removed from oil because it fouled the dual bed catalitic converters, around 1995 is when they took it out.
Who ever said that somewhat overstated the facts.
Oils API rated as SJ start in 1997 along with ILSAC GF-2
SL rating was adopted in 2001.
SM in 2004 along with ILSAC GF-4
None of them forced the
removal. Rather there was generally a
reduction in Zinc and Phosophorous levels with those oils that meet the ILSAC GF-2 and again GF-4 compared to the maximum earlier. The alarm bells (complaints and articles) really seem to have gone off with the implementation of GF-4.
Many API certified oils still have ZDDP. Those with ILSAC current GF shows on a spec sheet as Zinc and Phosophorous levels usually around 600-800 ppm (or .060 - .080). However there still are some oils with higher levels - they may be API rated but will not be current ILSAC GF certified. (Current ILSAC GF will be in the donut or use a starburst circle).
The better oil companies mix a package of additive levels that work together. Too much ZDDP or detergents can interfere with each other. Some base stocks need more ZDDP than others. The ZDDP is also not the only antiwear additive available. So while it has a good history for high temperature-high pressure protection there are others that are better in other situations, or newer and less tested (especially for racing situations).
I too have used Rottella products, most recently the T6 5W-40 in my Jeep AMC 360. They just changed the formulations this year so I'll reevaluate when I finish breaking in the new engine. And being a new engine, it shouldn't need or want the 40.
