Could anyone tell me what this problem might be? (See picture)

 

Looks like your CV boot might be torn and the grease is leaking out. Check that black plastic boot and look for a tear. Check inside the boot if it is a tear to see if you can see grease still inside. If so and there is no clicking or play in the CV joint, you can get away with a reboot and not have to buy a new axle. Info on a reboot here.

 

If it hasn't gone too long (not making noise, no play), then rebooting is waaay better than switching out that precision made axle with a piece of discount store junk...