omargrand

I have a 08 535 a week ago I seen a crack in my expansion tank also I seen oil in there as well took it to the dealer and the changed the expansion tank did a compression test also checked the head gasket. This morning I noticed a little oil misinf with the coolant. The car is running strong and fine no overheating. I have a friend with a 335 he stated it may be coming from the oil cooler . Any insight would be helpful, planning getting jb4 but wanna resolve this 1st