Hello, I'm not sure how your wife can distinguish the smell of oil but I'm pretty sure it's not that, or if assume that's true then the only possibility is that the water and the oil are mixed together and you have a leak in the heater radiator, in this case the last thing you need to care about is the leak because water and oil should not be mixed otherwise your engine will wear faster, among other things.
So first of all, check the bottle that contains the water, if you see black oil floating then that's a bad sign otherwise it's fine (you have to do that while the engine is cold !!!), after that you need to keep an eye on the water level after every trip, the goal here is to detect if the water is decreasing or not, you don't need to wait until the engine cools down because you can see the water level without opening the bottle.
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