Oil in the coolant reservoir why?
Bad head gasket and/or warped head and/or cracked block and/or someone dumped oil in radiator.
That might not be oil but instead transmission fluid.
There’s a transmission fluid cooler inside the radiator. If this cooler springs a leak, transmission fluid will contaminate the cooling system.
If possible, check the transmission fluid for proper level/coolant contamination.
Yes.. And lovin it