It looks like it was on the accessory belt, not the blower belt.
checked both wheels and yup boot leek on da driver side but not on the passenger sideI had the same problem on my last GP. Turned out to be the boot on the axle shaft had split and was flinging grease onto the belt which then threw it all over everything exactly like what you have. You should be able to track it back to one of the causes mentioned here.