Lose about a liter every 3 days, no smoke, no boiling. Coolant ratio right, no drips on the ground, what gives... Mostly does it after sitting all night.

 

This has to be a bad coolant seal that is allowing coolant to be put out the exhaust. You may never notice any smoke. Have you pulled the intake to make sure it's not an intake coolant seal? It could also be an internal seal.

 

have you looked at the weep hole on the bottom of the water pump? i've had a couple leak and not make it to the ground, also you should look around the radiator and heater hoses.

if you don't visually see any leaks, the next step is to pressurize the cooling system with a pressure tester, just about every shop should have one

 

I an going to change the intake gasket. Thought i saw a drip the other day onto the exhaust

 

that is another spot that can be hard to see

 

I knew a guy with a nice FB who parked it for years thinking it had a bad coolant seal and needed a rebuild. One day it started running very sluggish and after it was shut down would barely turn over and not restart. Water was flooding the chambers. I told him to pull his intake manifold and inspect the O rings and they were both shriveled up and cracked.He replaced them along with the manifold gasket and he still drives the car today

 

I did something similar on a loaded 94 f150. The guy sold it to me for 400$ and blowing black smoke like it had a broken valve. Replaced the coolant sensor, had a very nice truck. Of course due to bad previous maintenance it threw a rod, but i sold it for 450 afterwards....

 

i bought an Rx8 where it didn't start one day, and the owner took it to a "race" shop, and for $100 they pulled the dipstick, saw the condensation, and told her it needed an engine.

i put 4 coils in it and the rest of the major service, and had a nice running car