I've got a UV torch. It's useful for other things , such as spotting scorpions at night in the bush. They fluoresce nicely.Coolant also reacts to a uv/black light. Even when it’s dried up so that’s an option as well.
As for the black light , when I was a kid there was a kid's book where a mad professor had invented the electric dark globe. When you turned it on , the room went dark.
I digress...