OIL IN RADIATOR E46 M43 engin

Hi all..
PLEASE HELP
I have a 318i
2000 Model
M43B19 engine Single Overhaed Cam 8V

I have water in my cooling system bottle next to radiator. This engine doesn't seem to have a oil cooler for engine only for Auto gearbox.
Headgasket has Not gone as per several tests already performed. What can cause the oil to get into the radiator liquid????
PLEASE HELP
Thank you
Bobby