Do you mean the swivel housing? (shiny round part of your axle that allows truck to steer)
grease is leaking out of this?
regardless, if something has been leaking for a few weeks and you have a few more to go, then the level is low and you should add appropriate fluids. Its probably been leaking since before you noticed it. I dont think the grease in the swivels can leak unless something is majorly loose. Or unless the gear oil is getting into the swivels, and something is loose.
check for any loose bolts. get a wrench and try to tighten things. Add oil or grease. you cant overfill these things to the point of damage like an engine, so you might as well get to know your rover that much more and lube 'er up!
post pix if you want REAL help!