My car broke down last week, I'm so thankful for auto mechanics
I know what you mean, my best friend is a mechanic and does a variety of automobile makes but others work in specific areas.
Yeah my mechanic is a genius at mostly everything. What are some specific areas a mechanic my specialize in?
Well, for instance some only work on transmissions, etc.. of course their main role is to diagnose the problem accurately and quickly.
Okay I see. Luckily my issue was just a water hose and not a huge issue like a transmission!
Was it an item that may have been found during basic vehicle maintenance ?
I'm not too sure. I just noticed liquid leaking underneath and my car would overheat if I ran it too long. I was worried it was the radiator. 
So in your case it involved the repair of a specific part, but in some it can be the replacement of entire assemblies.
Yes I was glad it was only one part. But it still cost me more because of the placement of my hose. Most cars are above the engine, mine was below. More money spent on labor.
Many don't do the "scheduled replacement" of parts because then parts are replaced before any problem is observed and then why is the expense necessary, but yeah it always seems the labor is more