Looks to be some condensation. One way to be sure the head gasket is ok would be to conduct a compression test. Regarding the oil cooler, I've just replaced mine over the weekend. I would strongly recommend taking the front end off. The amount of effort and time required to get to the coolant lines running to the oil cooler, let alone the limited space, would be made up by taking the front end off and having perfect access; With front on; With front off; I know its a pain having to get the air conditioning re-gassed, but its also a good opportunity to replace the a/c drier aswel