Is it possible, then to get a stock Mopar catch can and put it on a car that did not have one?
....and maybe not be questioned when it comes to warranty work if ever needed?
It looks like my car has a plastic intake manifold.
What are the circumstances where heat is generated and how does oil bake onto plastic without melting?
You're mixing 2 different concepts. Direct injection engines have the baked oil problem on the intake valves - we do not.
In our 5.7L MDS Hemi engines, the vaporized oil is drawn through the PCV and into the intake manifold (no real heat to speak of), but some oil vapors collect and condense on the intake runners and don't get drawn into the cylinders to be blown out the exhaust after combustion. What happens is these droplets eventually build up enough to become 'fluid' which moves with the motion of your driving.
What some people will experience, upon slowing to a stop (deceleration) is a lagging/surging of the engine. Many people believe (me included) that the surging is caused by liquid oil pouring off the intake runner and into the cylinders.
I didn't like the behavior, so I
installed a catch can - it catches 2-3 ounces of oil a month on average (1200 miles), but mine is a 2008 with 94k miles on it.