Yes it's true. Hot Rod had a very descriptive article on it last year. It is because the oil companies are aligning their formulations to modern engines with roller cams, that do not require ZDDP. It's also cheaper for them to produce. It's also because they are caving to pressure from the big three because ZDDP is supposed to shorten the lifespan of catalytic converters, and they're trying to make cars to pass emissions for the life of the vehicle.
For you guys with flat tappet cams, you either should break in your engines with diesel oil, like 15W40 Shell Rotella, or use racing oil if you want lighter weight, because they have plenty of ZDDP. You can also go to a GM parts counter and buy an additive that adds ZDDP to your store-bought oil.
I read that Shell Rotella will stop putting ZDDP in their oil too, as diesel engine technology improves; but I don't know how soon that is.
I am building a 305 with a hydraulic flat tappet cam and although I used to break in engines with straight 30-weight oil, I think I will use Shell Rotella to break in this one, just to avoid problems.
