Does 1977 Eldorado require oil additive?

[Rockne Smith]

Local mechanic recommended I add zinc additive (I believe he said)  to Mobil One oil used in 1977 Eldorado 425.  He said valves need it.  Any thoughts?  Engine has 45,000 miles and runs like a top.  I don't know what oil was used prior to my change to Mobil One. 

[Eric DeVirgilis CLC# 8621]

Generally recommended with older engines not having roller lifters.

[35-709]

Don't know how much you really need extra zinc in a well broken in engine but it is worthy to note that, depending on which Mobil 1 you use, you may or not need extra zinc anyway.  Not all Mobil 1 oils are formulated the same as far as ZDDP is concerned.  For this reason I use Mobil 1, 15W-50 exclusively in all of my flat tappet engined cars --- year 'round (see my list below), Phosphorus is 1200 PPM and Zinc is 1300 PPM, plenty enough and at 15W-50 you can use it in the northern climes (maybe not Alaska  ).

Engines used in my cars below --- 2 - 472s, 1 '70s vintage Chevy 350, 1 '68 Pontiac 400, & 1 '73 Ford 460.
Not listed is the engine in the '42 Cadillac  that I sold shortly after I got it --- a pig in a poke --- a whole 'nother story.