Go on Amazon and get a decent UV flashlight and UV liquid detector fluid, make sure it's for the coolant you are running - there are different ones for green and orange coolant, oil, etc.
I've had a slow leak for months and found my coolant leak after two different shops said they "found" the leak.
It was the water pump. A drip from the weep hole that was very hard to see until I used the UV light. The hole and everything below it lit up like a Christmas tree.
It's on a D2. Your results may vary.