I don't think there's so much of a parallel between software design and working as an automotive mechanic. The analogous profession would an automotive engineer. The auto mechanic is more like someone who specializes in debugging and never writes code from scratch, in a way, but at the same time the analogy is even then a bit too flimsy and seems to break down.
Then again, I know only very basic rudiments of automotive mechanics, so I may not be the best judge in the world of such an analogy's validity.