My technician is the one who put it in place. So I bet he really put it alright. So if i fit a liquid cooler which is a hell of a expensive do you think the temp will play at 40 degrees C?
If the 'correctly fitted' stock cooler can't keep it cool at near idle loads a water cooler probably won't either.
Have you checked the cooler to make sure it's tight?
Shut it down and let it cool down and give it the 'wiggle test'.
Can you make the cooler wiggle on socket with just a small amount of effort?