[69nova]

Plastic intakes have the advantages of giving a smooth surface to the ports and airways which decreases any turbulence. But the main advantage is that they cost less and are lighter.
I have heard that GM has had problems with these intakes particularly sealing. In fact, some motors will exhibit hydrostatic lock due to coolant loss into the cylinders.
Motor Magazine may have been the source.
The other possible problem related to sealing is torquing the screws to obtain a seal without cracking the unit. Hopefully, the part has been designed with this in mind.
My apprehension is that parts are now being designed with the warranty in mind. What happens to those customers that keep a vehicle for 5+ years-into the 100,000 mile range? Everybody applauds some gadget that performs well on a new car but will it hold up to fatigue induced by vibration and temperature variations?

 

[69nova]

Consumer complaints in www.nhtsa.gov carries the info under "engine and engine cooling". Leaking of the intake manifold on 3.8L's.

 

[69nova]

What is the fix for these cases?
Except for a re-designed part, you are looking at recurring problems.

How I hate the methods of weight saving. In contrast, on my all cast iron Pontiac motor (400 cubes for my 73 Grand Prix), I had a hose blow while on the highway and before you knew it, the motor just ground to a halt. I let it cool, walked to a service station for a new hose and coolant and replaced the hose. Started it up and ran the car for another 5 years with no problems until I sold it. If you want to save weight, make the seats lighter.
And the transmission on that 73 was a real rock crusher.
An aluminum intake manifold would suit quite nicely.