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Ralph,
You must have read some of the same articles I did.

I also read of recommendations of higher zinc during break-in,
but also that today’s high detergent oils tend to wash the zinc
off the wear surfaces sufficient to negate the higher concentrations
in the oil.

What a mess......

What an informative thread. I've used T3 for years so it's cancellation is not good news.
I took the liberty of emailing Shell Technical support and asked the question whether T4 lacked the amount of ZDDP that T3 featured. The answer I got was that Rotella still had plenty of Zinc and was the best mineral oil for older engines. They also sent me a spec sheet, an excerpt of which I've attached.
Tim

Nice job Tim

Thanks Tim. That is the kind of information I was looking for. I'll switch back to Rotella for my next oil change.