Unidentified part

95 toyota 4runner sr5 3.0, 6 cyl

i have a part thats leaking oil. Its above the oil pan on the drivers side. Its round, about an inch and a half thick, 3 to 4 inches in diameter. It looks like a large tuna can almost, with a boths head in the middle. It has lines running to where the engine thermostat is. What is this? I have been told it may be an oil cooler, however I cannot find one that looks like this most are radiator type. I dont want to remove it until I know what im dealing with, and if it has gaskets that can be replace or if the whole whatever it is has to be replaced. I dont know what to search for.