It's an '08 RL with 140k miles on it. Around spring time I noticed my coolant level would drop from max to warning light level every 200 miles or so. It's now loosing that much coolant in 100 miles. I did the obvious searches for leaking and found nothing. At this point over 2 gallons of coolant has been introduced introduced into the system from constant topping off. With no apparent leaking. Stumped, I put UV coolant dye into the cooling system. This stuff glows like cartoon radiation under UV light and sticks to everything it touches. Anyways, I did a 100 miles or so with the dye in and searched every inch of the engine bay and I still can't find the leak. I've examined the water pump thoroughly especially. No hints of leaking. Can anyone suggest any ideas?