All the USA gurus are probably still in bed Ciaran!
No reason why you can't replace the brushes yourself, the paper clip method is the usual way it's done and it sounds like you forced the cover down before one of the brushes was all the way in. I'd say this is your first time to do this job, so it's just down to inexperience.
As a last resort, an alternator repair shop will pop the thing back together for only a few dollars. An experiened repair guy will have the unit pressed home in seconds.