Small oil leak at valve cover 912 ULS

Hi, I found a small oil leak at cylinder #3 valve cover.
The engine has only 6 hrs on hobbs, It happened after a one hour flight in cold weather.I have an oil cooler thermostat fitted but I forgot to cover a small surface of the water radiator before the flight. During the flight, I had noticed a wide temp variation of CHT but within limits.
I am wondering if this could be the cause of the leak. I have checked the cover torque, it was all good.

I will do an engine ground run up before next flight.