If you want to service the freehub, remove it, pop out the seal, and run solvent through it. Dry it and use a heavy oil to relube it.
shimano used to make a tool to take apart their freehubs. Based on a Zinn article I bought one and replace the spring in my freehubs with a heavier one made from piano wire so I could pump grease through them. I use this tool to pump in a light grease every other overhaul.
http://www.loosescrews.com/index.cgi...d=453593013705