Good day

so i found some oil in coolant tank.

first mind it was from some old tube that was replaced because it leaked coolant.

but after 5 cleaning times with Wynns cleaners it did not help.

Oil appears in coolant tank after about 500-600 km. it is not much but still top of coolant is black.

Coolant tank does not give CO.
Oil in the engine stays in same level and color is normal.
coolant level is the same.

so few possible issues:
Engine brake - hope not as it drives normally.
Engine head gaskets - could be but there is no CO so maybe not.
Gear box - did not check oil in it but hope not.

and the winner i guess is oil cooler.

could be gasket faulty or could be oil cooler went down and has some small hole.

so any possible information how to change gasket or remove that oil cooler and bring it to check.

it should not be difficult but still want to be sure what needs to be done.

Thanks.

situation looks like: