Also the perfect spot for a screenwash leak which can also feel slippery, and given the colour that's my guess. Assuming you have headlight washers, it could be leaking from the hose joint between the pump and the bumper hardware, or its quite common for the screenwash pump to leak from one of its two seals.
The gearbox cooler hardware is on the opposite side of the radiator, and that oil will be brown / grey. The two radiator hoses are on that side, but coolant should be pink rather than clear.
Next step is to pull the undertray off. You should be easily able to see whether its dripping from the engine, radiator, or screenwash tank
