Cat 322L Hydraulic oil showing up in coolant

A relative of mine picked up a Cat 322 L knowing that hydraulic oil was turning up in his cooling system. He figured it was the oil cooler and replaced it.. Now he's still losing oil and it still seems to be turning up in his cooling system.. Not sure if anyone here has seen this before.. Any help would be appreciated!!!

Cat 322L Hydraulic oil showing up in coolant