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  1. M

    Oil and Filter Question?

    I have an 1998 Cadillac Deville 4.6L N* 45,412 (Original miles). I am the second owner, and it has been well looked after. My question is this... Being a flat tappet motor with 300HP do I need to add any Zinc to my oil since it was originally designed for the SH specification? I've been...