[chittychittybangbang]

This is a common place for oil leaks, this article shows how to replace the o-ring. The only real trick is to rotate the cooler as you pull it out due to clearance.

http://www.myturbodiesel.com/1000q_how_to/a3b4/oilcooler.htm

Other common places for leaks: valve cover, egr weep hole, engine block breather hoses, oil pressure sender. My oil pressure sender was actually leaking out of the middle of the sender. All fixed now.

 

[chittychittybangbang]

Always clean the area first and then confirm where the leak is coming from. Oil tends to get blown around and can move up, down, sideways, etc.