Oil flow is from the boss on the crankcase behind the oil cooler housing to the oil cooler and thence to the cooling circuits on the heads.
Remove the cooler housing and unbolt the hoses from the heads and the case and remove aye entire mess.
Remove the cooler from its housing and disconnect the hoses, back flush them with kero and then water and bow out with compressed air. Then do the same with the cooler itself and reassemble.
Pete