Otherwise the car runs great. I'm a mail carrier and it gets lots of use. I have an appointment for another look but they have never serviced a subaru and seem to be stumped.
95% chance the problem is not 'Subaru specific' - ANY mechanic could knock a connector or hose loose, or misalign an occasional timing belt on ANY car.
If it started fine before the work, new gaskets would not create this problem. Not IMPOSSIBLE to be a new problem, just more likely they created it with the work they did.
can you describe exactly what it's behavior is when it's failing to start? is the check engine light on?