Hi Dan,

I guess the final resolve might be pulling the intake back and running a straight edge across the face of the manifold.
I have seen many a cast iron manifolds go into twist. I’m sure it’s possible for aluminum ones too!
It’s impossible to spot warp without a test with a straight edge. Especially on the car still.
A person cannot just sight down the front and spot each flange in relation to each other’s bolt holes.
If it is warped the studs are hold the manifold.
Their not made to twist it back flat very much if at all.
A manifolds tube structures are quite massive by comparison.

Another thing I want to bring up is the “type” material or even the amount of gasket thickness that I have noticed between manufacturers.
I have taken off a couple manifolds where the gaskets were obliterated in more that one place.
They had holes that were literally scattered, like Swiss cheese in them!
Surprisingly just how many thin small holes of deterioration that hadn’t even lead to the outside.
I surmise that these gaskets were very thin to begin with and got thinner with their aging.
We are dealing with gasoline and engine oil vapors that contain cooked out petroleum and their chemical additives!
The choice of materials to use is not so basic!
Just to add some perspective to this vacuum physics thing … with 20” of idle vacuum, there is a column of air, one inch square, trying to get inside that vacant area.
It might not seem like much, but it’s 200,000 feet high!
It’s that last little split between the outside and inside that we want to keep to a minimum amount of exposure.
It’s the reason for thin but with some manufacturers, it’s an obsession.
But like most things in life, there are limits and compromises!

I have purchased parts store Over The Counter gaskets before from known brand names and store brands and there are differences like cuts of cloth for dress suits!
These are for mainly non-critical gaskets!
Head gaskets are made to higher standards, due to their locations, but the demand of the job at hand is the same!

Now the original gasket on an engine faired better than the others that were right out paper thin.
Those told me they were non factory or even OEM.
What I’m saying is, the factory gets the best shot at making the car right, the first time!
Paint jobs, welding and assembly!
Everything is made to fit, “within reasonable tolerances”, but they even used thicker gaskets?
Why … for the reason just stated!
They wanted it to get off the assembly line and past the dealer for a few years!
This is where early Volvo shined because of several combined efforts throughout the corporation!
Not perfect, because perfect doesn’t exist, but the stars do align for a short time! (:)

Do not put on the thinnest gasket, especially on a used heat stress relieved engine unless you know all is flat!
I do not use Fel-Pro intake gaskets. They make good gasket material but in our application or with used manifolds, I would not recommend them.
I have to track down Victor-Reinz products for being a more “substantial” gasket material, IMHO and more like what the factory used to get the parts to seal. It’s thicker and more forgiving.
They are a little harder to find, for whatever reasons beside profit to chain stores!
I think they are worth a few more dollars, on my bottom end!

So … if you decide to jump under the manifold, consider all that air standing above your head and squeezing on your body’s suit!

(:-) Your gasket is only skin deep, but it renews itself!

Phil