New Intake Manifold - Installation Discovery

I'm working a small amount on the intake installation in the evenings.  I work for a bit and then take a break for the evening as it is rather hot in the garage and I'm in no hurry to get the job done.  

While working on the car last night, I took a picture if the engine before removing the intake.  I've become familiar with seeing the blue intake on top from when I painted it years ago.  I expect it will look quite a bit better with the bare aluminum intake.  

Once I removed the intake, I found the gasket was in horrible condition.  There are two cylinders (#6 and #2) where the intake gasket cracked and caused very clear leaks to the top side of the motor.  There are several cylinders (#3, 5, 6, and 7) with leaks to the interior of the engine.  The intake slid over so that it actually blocked the ports on cylinder 6 and 7 to a degree. 

I'm quite shocked at the condition of the intake manifold.  The front two bolts felt a little lose when removing them but the rest did not seem too loose.  The center bolts were tight but they did not feel over torqued.  I'm not sure what caused this to occur and how long it has been this bad.

I'm a bit concerned about the situation as I purchased the same FelPro 1250 gasket for the new intake.  I remember installing the intake last time and I was incredibly meticulous about every task of installing the components as I wanted it perfect.  The following picture is from the install and shows the gasket adhesive, rtv around the intake ports, and everything looks perfect.  I can only assume bolts came loose over time or were not torqued properly and slowly the gasket deformed.

This explains the difficulty I have experienced when trying to tune the carburetor.  I would reject the carburetor and it would seem better but then be lean again over time.  This is concerning as I was likely making certain cylinders incredibly rich so the O2 reading averaged out properly while certain cylinders were very lean.

The second item this explains is the burning of oil.  I thought the engine was picking it up through the PCV valve.  I did not expect a leak between the lifter valley and intake to be the cause.  It is most certainly the main cause of the problem.

Lastly, I noticed before when performing a compression check that cylinder 3 and 7 had strange looking spark plugs.  I think those two were lean from breaks in the intake manifold.  Looking back at the pictures, cylinder 5 was also darker than the rest and that is likely from oil entering that cylinder because the gasket is all deformed. 

I'll be happy to get this job done and see how the engine runs.  I'm curious if I will notice any improvement in the performance.