When perfection isn't the goal

I have a dilemma.

Students write a lot in my classes, and sometimes their writing provides excellent examples of concepts I'm trying to teach, so I frequently type up sentences or paragraphs from students' writing to share with the rest of the class (anonymously, of course, although some students speak up and identify their work). I choose work not because it is the best or the worst but because it illustrates a particular concept or technique, even if it's not perfect.

And here is where the problems arise: suppose a certain paragraph from a student's paper includes a really interesting example that I'd like to share with the rest of the class, but it also includes some small errors in grammar or spelling. If I'm trying to get students to pay attention to the way one of their classmates incorporates quotations, then I don't want them to be distracted by the fact that a comma is missing or an author's name is spelled wrong.

Is it better to silently correct the small errors or to leave them alone and display the sample warts and all? Which is more important: clarity or accuracy?

My practice is to silently correct small errors unless they provide opportunities for learning, but I've never felt good about this. On the other hand, I hate to put a piece of student work up there and point out everything it does wrong; I'd rather focus on what it does right.

Which is better? Any suggestions? Maybe I ought to ask the students.