I do not own an AVEO , our car is a Sonic . So I do not know how much they have changed . But I will take a look when I get home .

It may be in the brake booster it self ? Where does that hose connect to the engine to get the source for its vacuum ? Can you take a photo & post it ?

In the mean time , you might try the following test . Un-hook the hose at the source . Suck on the end of the hose , as hard as you can . Then try to put your thumb over the end of the hose , to hold the vacuum . Then release your thumb . Did it loose all the vacuum ? Or hold that inside the booster ?

I am wondering if what ever fitting that the end of the hose attaches to , at the engine , may have a check valve inside the fitting ?

I looked at photos of the booster , on line . The fitting at the booster appears to have no check valve at that point ?

This check valve appears to be a " universal part , and not specific for your car .

Dorman HELP 80189 - Power Brake Check Valve And Grommet | O'Reilly Auto Parts

God bless
Wyr