I totally agree with the comments about buyer beware. Back when all the SM oils came out, I contacted many of the oil mfgs and was told SM was fine for flat tappet engines. Now we now better. Even after the issues came up, when I contacted Amsoil, they wouldn't tell me how much zinc was in their oil, but it was enough. I had two pushrod failures on Amsoil diesel oil back then, change oil to another brand and no more problems.

I like to run the motorcycle oils, as they have all the additives you need, without the extra stuff in diesel oils that you don't need.

I like this in 5W40 for drivers and our motorhome and in the 20W50 for the TT340 Chally.

http://www.castrol.com/castrol/sectiongenericarticle.do?categoryId=9021703&contentId=7040544