In reply to:

Yeahbut®, you'd hope that the mechanic *did something to it before you take it back home. And if you're *real lucky, the mechanic did something that improved its performance.

OK, spell this out nice and slowly for me please. My response to wsieber focussed on the idea that "bring" is often used to describe a situation where the thing brought is left behind, while "take" is used for situations where the thing taken is not left behind. I did not disagree, but said that, as I saw it, a case could be made for saying that the difference did not hold true for the situation I described.
Here is where I need it explained monosyllabically for me: What does the fact that the car is worked on have to do with it? I was simply, and solely, addressing the issue of whether or not the item taken somewhere was taken back again. The issue of what happened to that item is, as I see it, completely outside the parameters of my post. I look forward to being enlightened as to what I actually meant in my post.