We have a 2015 Impala that my wife drives daily. Recently it's gotten to where it kinda stumbles/hesitates/shimmy's when you slow down behind a vehicle and apply throttle. Sometimes it does it from a stand still as well. I've hooked it to my scanner and it doesn't show any codes, any misfires, etc. I decided to try cleaning the throttle body and cleaned it best as I could. However, I noticed that the intake sucks vacuum through the threaded insert for the engine cover. I'm assuming that intake is bad, doesn't make sense why it would suck vacuum through a bolt hole but 🤷
This is the bolt I'm talking about....
View attachment 166560
The bolt head for my 2014 Impala 2LTZ (purchased new - original bolt) uses a T-30 socket to install / remove the bolt.
The bolt head in your picture looks like it is damaged, perhaps from overtightening?
If you are positive the hole is sucking air (how do you know?) - you may want to use high temperature epoxy to seal the hole and not use the bolt.