GM dealers sell a product  called EOS (Engine Oil Stabilizer) which
is rich in the missing ingredients. Crane apparently recommends using
this additive to modern oils for use in older vehicles. Sorry, lost
the reference to the article.  I do think I forwarded it to the list
some time back.
On Sep 13, 2007, at 6:07 PM, Automatic digest processor wrote:

> Date:    Thu, 13 Sep 2007 22:11:14 +0000
> From:    Todd Last <rubatoguy@COMCAST.NET>
> Subject: Re: DOn't use SM rated  oils    Re: Flickering Oil Light
> 84 auto
>
> I thought you were not supposed to run SM rated oils because of the
> lack of zinc additive?
> The SM oils have very little zinc and phosphorous (<0.08%)
> supposedly to help keep catalytic converters from fouling - however
> the lack of zinc is causing premature valve train wear in some
> older vehicles.
>
>