The N500 base oil spot premium over futures narrowed to +780 CNY/t—down 40 CNY/t from +820 the prior day. This is not demand recovery, but a reset of import substitution timing: Sinopec Maoming’s scheduled N500 unit maintenance, set for Oct 15, has been postponed to Oct 22, delaying domestic supply shortfall realization. Concurrently, three N500 cargoes from SK Korea and ADNOC UAE are scheduled to arrive at East China bonded terminals between Oct 18–20, pushing weekly bonded入库 to 21,000 tonnes—the highest in six weeks. Supply-side disruption weakened spot premium rigidity. Fuel oil futures surged 3.71% to 4,947 CNY/t, directly raising the economic threshold for N500 blending. At current blend ratio (N500:FO = 75:25), per-tonne lubricant blending cost rose ~112 CNY, eroding price competitiveness of domestic mid-tier lubricants versus imported premium grades. This fuel oil rally tracked Brent (+3.78%) but with steeper slope—indicating Asian marine fuel demand elasticity is shifting from shipping toward industrial blending. Asphalt dipped 0.36% to 4,454 CNY/t—not just road construction seasonality, but evidence of lubricant chain transmission friction: asphalt refineries often co-produce industrial white oil and HVI base oils, and their operating rate has fallen—reflecting broader margin pressure across co-product refining segments. Downstream grease plants simultaneously reduced N500 procurement intent—natural rubber and butadiene rubber futures fell 0.08% and 0.25%, reflecting flat formulation rubber demand and dampening upstream base oil restocking. Conclusion is unambiguous: import substitution remains intact, but its inflection point has shifted upward. A sustained N500 premium below +750 CNY/t for three days triggers SNSUC’s client import price-locking window. If fuel oil holds above 4,900 CNY/t, East China blenders will accelerate shift to API Group II+ routes—forcing N500 imports to pivot from ‘volume replacement’ to ‘quality substitution’. Key risk: if Maoming maintenance slips past Oct 28, the +780 premium could collapse rapidly to +620 CNY/t, sharply increasing importer inventory turnover pressure. SNSUC Research Institute recommends: hedge strategies should anchor on the fuel oil–N500 spread (currently 4,947 – 4,454 = 493 CNY/t); a break above 520 CNY/t warrants long N500 futures to hedge blending margin; importers should defer execution of mid-to-late October vessel schedules and prioritize bonded stock drawdown; ESG carbon footprint services can be embedded into newly arrived ADNOC cargoes to lock LCA data for EU REACH compliance filing.