When would one need to rebuild a caliper?
 

After seeing these pictures, someone told me the pistons look like they are worn and need replacing. What's your opinion?

<img src="http://pictureposter.audiworld.com/70933/img_0235.jpg">
<img src="http://pictureposter.audiworld.com/70933/img_0237.jpg">

I thought they look just fine myself, but since this somebody supposedly really knows about brakes, I'm now worried...

seals and bleed screws are pretty cheap, might as well replace while the calipers are not installed

I was told I need new PISTONS though, which is why I'm so worried. Do they look off to you?

tough to tell if it's rust or dirt or whatever...
 

...but when they are out for the seal replacement, you can clean them up good and give them a thorough inspection. The critical part of the piston is not the part that touches the pad, it's the part inside the seal. if that has wear or the sides have wear, then I'd consider new pistons. If not, put them back in.

Thanks for the response!

Any tips for dual piston calipers?
 

I've got to replace my ripped seals this spring. Hopefully they don't rust up before then. I've heard that it's pretty hard to get both pistons back in, because as you push one in, the other wants to come out. Or is this not an issue when the brake line isn't hooked up?

Put a block of wood or something in there to keep the pistons from moving...

it helps to have the bleeder open too.