S8 losing coolant

Well, it seems the loss of coolant has been speeding up i think. Reservoir is dry this morning.

I dont see any leaks, nor do i smell hot coolant anywhere.
I suppose next step is to put some dye in it, pressurize the system and see if i can spot anything around the engine or reservoir itself.
no oil in coolant, or coolant in oil.

Anyone have this happen? Car was not overheated in our ownership, has just over 80k miles now.
Dont think its headgasket (i hope i should say)
Any other specific parts to go over?