The grease is seperating. The lighter greases tend to do this more often than the thicker ones, especially with warmer temperatures. Also tends to happen when the gun has been sitting for awhile. Grease quality would also make a difference.
If you pull the plunger back on the grease gun, you can take the end off and stir the grease inside the gun with a screwdriver, rod, or whatever. As long as there hasn't been alot of leakage, it shouldn't affect the lubricating abilities of the grease too much. If the leakage is excessive, I would put in another tube of grease to be on the safe side.
How long does your gun normally sit between uses?
