All the recall information for Aveos are in a sticky in this section of the forum and the 2004 only list an issue with the seat belts. I found a thread on another forum Timing Belt Warning Issue for all Aveo Owners - Chevrolet Forum - Chevy Enthusiasts Forums where there are many people who had serious engine damage because of timing belt issues. Your mechanic seems on the level with everything he is saying with all the problems everyone else has had with this particular model. It might be risky to fix it reading what other issues people have had.