Been chasing a slow coolant leak...Was praying it was not leaking into a cylinder. This X5 3.0 has had two head gasket jobs already.... I poured 1/2 oz (half a bottle) of UV dye and ran it for 2 days. Then at night, used UV glasses and UV light and found my leak! turned out to be my heater control valve, which in my case was an OEM unit that I rebuilt with new seals and installed a year ago.

A replacement unit has been ordered.

The UV coolant leak kit is great at finding leaks. Avail on Amazon.