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I believe what you are seeing is the EGR passage. The EGR valve is mounted on the right side of the intake and allows exhaust to flow back through the intake tract to cool combustion temperatures, reducing NOx and slightly raising fuel mileage.
It's common for EGR passages to become restricted because of the carbon flowing back through them, plus the temperature of the exhaust coming in will cause blowby gases and oil in the intake to gel up a bit on and in the tube.
If you aren't having any performance issues and aren't setting an EGR code it probably isn't to the point of being an issue yet. If it does set a code or it's just something you want to clean up before it becomes a problem then you can clean the passages with some carb cleaner, in many cases the valve would have to be removed and something pushed through the tube along with the carb cleaner to get it all out.
The Service Engine light came on and my local service center checked the error code, which pointed to a bad EGR valve. I removed the throttle body to facilitate replacing the EGR valve. The rear tube appears clear but the front is clogged. I will try to clean the front tube as best I can. Thank you for your answer, it was very helpful.