I just noticed a small amount of engine oil in the radiator fluid of my 2004 Land Rover Discovery for the first time. There’s no radiator fluid getting into the engine oil, and the engine still runs fine. This started right after I swapped out the 220-degree thermostat for a 180-degree one. I’m thinking that with the engine running cooler, there might be less expansion and a weaker seal, which could let a bit of oil leak into the radiator fluid. The oil only shows up in the radiator fluid when I’m driving, not when the car idles for a long time. That makes me think the oil is getting in only when the engine oil pressure is higher. Could this be a sign of a failing head gasket, or is there something else I should check?