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.

If insurance claims records are accessed, there will usually be notes like "the insured vehicle is fully responsible for hitting a fixed object" or "third-party liability insurance payment." We can roughly reconstruct the accident scene based on this and cross-verify the stress points on the vehicle's frame with paint thickness gauge data.