Just posting these links so I dont have to search again when I replace mine
http://www.jeepin.com/features/rearmain/
http://www.neow.org/rms1.html
http://tek-tonic.com/rearmainseal/
http://web.mac.com/donpryor/oil_pan_rear_main_bearing_s.html
http://www.dailydriventj.com/forum/viewtopic.php?t=811