What motor oil to you guys use? I thought this was a simple question a few days ago, but things have changed. I bought my 77 Trans Am in 1986 and have pretty much used the same oil every year - Valvoline or Pennzoil 10w-40. When I went to buy it over the weekend, I couldn't find it. I searched some auto stores on the internet and they carried it on-line, along with Castrol 10w-40, but the Napa and O'Reilly sites both said that the oil "Does not fit your 1977 Firebird", with no further explanation. What?? Going down the rabbit hole, I found out that the motor oils of the '70's, '80's and '90's included an additive that has since been removed - Zinc dialkyldithiophosphate, also referred to as Zinc or ZDDP. Apparently, the older engines need this additive, especially for the cams. A couple auto stores carry Lucas "Hot Rod & Classic" oil, which contains zinc, but the guys at some site I visited (maybe Bob the oil guy) claim that it contains too much zinc. I also found that you can buy a ZDDP oil additive. Any thoughts and/or suggestions? Thanks