The 2014 Highlander V6 is the 2GR-FE: 270 hp, port fuel injection, one of the most durable engines Toyota has built. Fuel sprays across the back of the intake valves on every cycle and keeps them clean, so the walnut-blast decarbon service quoted for this model online is not a 2014 expense — that advice belongs to the 2017-and-later 2GR-FKS. What this engine does do at high mileage is seep oil, usually from the timing cover or the water pump.
With the engine warm, look down the front of the block at the timing cover seam and at the water pump (passenger side, low). Dried oil crust or wet coolant residue means a seep already in progress. Also pull the dipstick: clean amber or light brown, at the full mark.
Est. cost: $400–$700 water pump / $1,200–$2,000 timing cover reseal
Source: Toyota 2GR-FE service pattern; MY2014 powertrain verified against Toyota specifications