Trace of oil in coolant reservoir?

Yep, the oil cooler will allow engine oil to enter the cooling system, here is a guide to help you see what's going on and I have included the oil cooler replacement instructions as well.

https://www.2carpros.com/articles/engine-oil-inside-the-radiator

There is also an engine cooler system thermostat which I would change if there were sludge inside the engine, please change the oil and filter once the job is completed as well. Check out the images (below). Let us know if you need anything else.

Thanks for your help, Ken. The mechanic is saying gear oil is mixing with coolant. The solution that you propose is also applicable for gear oil leak?

Chassis number: WA1AGDFEXED011656

Many thanks.

I am not sure gear oil can get into the cooling system only engine oil. Can you confirm it is gear oil?

Please see the video I have uploaded to YouTube.

https://youtube.com/shorts/Wbz2TSxFyxE?si=lk2vz7mxBjANG46e

Another video sent by the workshop.

https://youtube.com/shorts/p2ubhpMN1U0?si=Xbd8dj_rIdGk6CYC

The super charger is making noise, and it could be leaking into the cooling system which means you need a new super charger, this is a sealed unit so there is no way to check the oil level.