98 mustang Gt 4.6L V8. I have engine oil in my coolant resovoir. I had my heads checked for cracks and replaced my head gasket.Still have same problem with engine oil in my coolant. Strange thing is, it is just a one-way leak because I have no coolant in my engine oil. I was told my OEM oil cooler was defective and leaking oil into the coolant. Im currently waiting on that part to ship to my house. Is there any way to check my old oil cooler to see if it indeed is defective? Also i have lots of "sludge" build-up in my coolant resvoir and radiator from the oil and coolant mixture. Should i replace my radiator? Also what is the best way to thoroughly flush out the “sludge” from the cooling system?

Anyone had this problem before?