Oil leak from engine oil cooler

[jwtt2008]

Hi, I have a Subaru Impreza MY16 with around 150,000 km. I initially noticed an oil leak from the engine oil cooler, followed by a low engine oil warning. After topping up the oil, I discovered oil in the radiator a few weeks later. What tests should be done to identify the underlying issues, and what steps should I take to fix the problem? Thanks in advance for your advice.