Good Day dear friends,

Due to my lack of experience with the M156 Engine, I'm in need of some advice. The car is from 2007, Daily Driven almost 130KM to work and back, and currently at 180,000 KM on the Odometer.
As much I love the car, at certain times she is giving me nasty surprises which drives me crazy and at certain situations the garages here hasn't been very kind to me either with the expenses.
I seek your expertise and advice here, as I feel the initial diagnosis and the observations given aren't really connecting the dots for me.

Issue
I recently started getting an intermittent Check Engine Light. By Intermittent, I mean It will stay on for 2 days (approximately 2 drives with CEL ON, and one day No CEL - and again next day CEL ON).
After visiting the garage they ran a scan and the following errors were shown.



The Major error was suggested to be the P0191 Error.
The garage's mechanic suggested that it's a sensor based error, not something that affects the Perfomance as of now, opened up the front engine cover and worked on the below part.
Apologies in advance over the engine's dusty state, It is a helpless situation with the current sandstorm weather and continues daily drives.

The part in reference is what's highlighted by the yellow square. There was a black Hard Tube going from the left Red Circle to the Right Red Circle. It was an L shaped black plastic tube.
He removed the said black tube and connected an Aquarium tube to the left end asked a mechanic to Rev the engine, and showed to me that on the end of the tube there is no vacuum (suction) nor a push along with the REVs suggesting that the part is not functioning as it should.




The mechanic (who has been much supportive previously) suggested that the tubes in the vicinity needs to be inspected all the way to the manifold - and the error maybe caused by a certain flap inside the engine not opening as it should due to this lack of air / vacuum.
He then suggested that the manifold needs to be opened up to trace the rest of the tube and replace them if they are brittle and cracked - which he said might be the situation inside - and opening the manifold now may cause further damage or open up avenues to further surprises.
Opening up a tricky avenue as this is always a risk as the parts for W219 are not easily accessible in my state and while the parts a are sourced, the car may sit idle at the garage collecting dust / sand in places it shouldn't. So it is always smart to locate at least the availability of the parts before entering any section of the car.
He assured me that this will not affect the Perfomance in any way and if the issue becomes a bigger issue to the point where we need to open up the manifold - let's take the risk at that point and prepare ahead for the repair.

He proceeded to check the vacuum tubes once more with idle and REV state, then sealed both the open ends with tape and closed the engine cover without fitting back the tube as it too had a tiny crack in the middle.
I have not felt any change in Perfomance, and the CEL situation is still the same as before - intermittently disappearing on every third day.

I would like to have some clarity on my situation, and some advice if anyone has any experience with this.
Thank you for your patience and time in advance.