Right rear brake leak

[apok]

My 2004 GP GT2 had its low break fluid light came on earlier this week when I was leaving work. Looked at the ground underneath my car and noticed a small puddle inward from the right rear wheel. Had the chance to take the wheel off and look around this afternoon. It appears the seal behind the piston is leaking (pics available here: Photo Album - Imgur). It looks pretty dirty/corroded under this seal.

Is it possible that replacing the seal will fix my problem, or will I need to replace the caliper?

 

[dsmuts]

I'd be a lot easier to just replace the caliper but you could replace the seal.

 

[apok]

Is there normally some brake fluid contained within that seal, or is it just supposed to protect from dirt and corrosion?

 

[dsmuts]

Is that the boot that holds the piston in? I can't really tell from the pics.

 

[apok]

We're looking at the back of the caliper where the torsion spring for the parking brake is. The attachment has a top-down view of the caliper.