Truck Repair: stc 14 litre, oil cooler, engine trouble

Question
i have stc engine trouble the engine was rebuilt ,it has problems of bending pushrods every 1000 kms ,and it is mixing oil to the radiator

Answer
Oil in the coolant:If new liners were installed the probably the oil cooler but it usually mixes both ways if its the oil cooler.Have the chemicals been kept up in the coolant??Electrolysis will pit the liners.Does it bend the same pushtube or different ones?