I have a Delta shower head that continues to leak. The whole shower was installed 3 +- 1yr (new house construction). I pulled the shower head off, left it off for a while, and realized that it continued to drip. I therefore assume the problem lies in the valve (or a gasket). I turned off the water and tried to pull the valve apart, but didn't want to destroy anything so I stopped when it required a bit of force. I've got some pics, but my question is what part do I need to fix the leak? And ultimately, how do I fix it?

P.S. I've never used this site before...Let me know if my link doesn't work for my pictures. I can find another way to post them.