That's what happens if the dust cap is slightly bent. There is a lot of grease at the end of the hub most likely, it gets hot, gets a little more runny and if the dust seal is bent at all (from a shop pulling it off) then it leaks out slightly. Pull the cap off (and hub if you want to check the bearings and re grease), make sure it's round, clean off cap and hub, use a little RTV around the dust cap and tap back on.