The rear seal is leaking. This can be due to too much grease in the hub. Do you have bearing buddies? Pull off the rubber hub cap and look to see if the spring therein is compressed. If not, then you're likely losing too much grease to risk trailering. I would pull the hubs and look inside at the bearings and races for wear. If worn, then it is time for new bearings and races.
On my EZ Loader, you can purchase the hubs for around $50 with the races/bearings already pre-packed from their web page. The cheaper way would be to punch out the old ones and replace with new, including the rear seals.
There is way too much to learn about bearings and hubs than can be said here - check out this site for great info....
http://www.diynetwork.com/diy/bo_mai...277898,00.html
or here...
http://www.iboats.com/bbboard/bbBoar...ewforum;fid=22
or here...
http://www.rockettrailers.com/GeneralMaintenance.htm