We use two steps: 1. Insert a medical-grade endoscope through the spark plug hole to visually inspect cylinder wall scratches and carbon buildup on the piston top; 2. Extract an engine oil sample to check for large metal debris or emulsification (caused by coolant leakage).

We maintain an absolute skeptical attitude. In addition to regular visual inspections, we focus on checking for sediment accumulation around the sunroof drainage channels and look for water stains under the A-pillar trim and front floor mats. This is the only effective physical evidence to determine if the sunroof drainage holes are blocked, leading to hidden leaks.

Our bulk discounts are not simply calculated by the number of units, but by shipping batches. Typically, consolidating enough for a 40-foot container (which can hold 2-3 vehicles, depending on size) can waive some logistics fees; purchasing more than 5 units at once triggers tiered discounts.