I just want to add my 2 cents. I have a 2008 Chevy impala and I just happened to accidentally stumble on this post
My impala has been having this same issue for years.
The actual part is called, power brake booster front seal. I order this part once a year because for some odd reason it fails constantly
If you're getting a check engine light with a lean code, chances are you will need that part.
The tricky part is no one carries that part not even the dealership. You will have to go to a independent parts place or company that actually we manufactures power brake boosters for cars. That's where I got mine and I order mine every year. So if you have time just Google remanufactured power brake boosters and something should pop up. I actually order mine from a place in Indiana and I am from Atlanta and he already knows my name and everything and I just ordered every year
It's definitely a design flaw by GMC and it probably affects every GM card and that 2006 and 2013 generation of GMC cars
