You are probably due to change the crossovers anyway, but I’d want to try to find the leak first if I could so if there are any additional hoses to be replaced, you know in advance. You can try sticking a boroscope down into the valley next to the oil filter and look for fluid, and maybe feel around the rear crossover with your hand.
There are several hoses that run off the passenger side of the rear crossover and into the heating system. Some go into the heater core in the front cabin, and then some run down along the bottom of the passenger side of the car to the rear wheel arch and into the aux heating unit in the rear cabin.
Maybe put a pressure tester on it if you have one at your disposal. And/or some UV dye - make sure you get the stuff that is dexcool compatible.