Every once in a while I smell just a hint of antifreeze. I've felt all around the expansion tank and find nothing. Whatever it is never makes it to the ground. The octopus hose looks excellent.
I see that I still have the stock plastic thermostat housing. Likely candidate? No clear evidence of a leak but something has been collecting dirt below the housing and near the water pump. 2004 with a bit under 35000 miles.

 

Why don't you 'borrow' a cooling system pressure tester from your friendly, local auto parts store? A few minutes effort on a cold engine and you would know where the leak(s) is/are.

 

+1. However, make sure one of the caps fit before you leave. The Jag has an odd (for the US) cap and not all the auto places have that in their kit.

 

The 'universal' one fits universally. Most likely, none of the others will.

 

+1 to pressure testing.

For a mysterious smell of coolant and a loss that never appears on the ground, look for a tiny pinhole or crack in the base of the Expansion Tank.

One in this location allows a very small amount of coolant to drop onto the hot exhaust manifold and vapourise immediately leaving no sign when the engine is not running.

Graham