Cooling System & BHG test
Rent a cooling system pressure checker from Autozone or O'reilly.
Fill your radiator, make sure you fill it with the air bleed screw open (12mm wrench).
With the engine cold, hook up the pressure checker and pump it up to about 15 pounds. You should hear any leaks easily since the system will be at pressure and yet the engine isn't running. No leaks? Move on. If any leaks, correct them first.
Again, with the engine cold, press up the checker to 15 pounds. With it still attached, go ahead and start the engine. It is not necessary to remove your thermostat. With the engine running, look at the pressure gage. Is the needle fluctuating? Bad. Is it steady? Not a BHG.
I REALLY doubt your new RL has a seeping head gasket.
Last OMG check. Crack your oil drain plug. Open it a ways, but don't remove it. Does any coolant come out? Bad.
Anyway, if you are losing coolant, not getting white smoke, and it's not in your oil, it's simply leaking somewhere. Differential cooling lines? It may be a slow leak, but it's probably slowly going away.
Good luck bro.