Warning , unless you know your dealer has a good reputation , you may want to avoid using dealer , but being that your under warranty , its a tough choice .
But the way to find the leak is to use a mirror with that flash lite , then where to look is at the bottom of the water pump pulley & just behind , there is whats called a weep hole that will allow coolant to come out as the seal fails , if this goes on for long , the bearing fails & the fan can come lose & fly around & get into all kinds of stuff , the dye is used in case there is so much fluid in the area , that you need to see the difference between the old & after adding dye to look for , yours looks clean enough that you should be able to fine with the mirror & flash lite , to help when it only leaks occasionally , having coolant pressure tester , it goes in place of the rad cap & then you pump pressure [ 5-10 lbs ] into cooling system , to help find leaks .
If the dealer wants dime one , go to a Cummins dealer , buy a pump do it your self , one of the easiest things that you can do is replace the water pump .