AWD CX-5s use a rear coupling unit with its own fluid. Mazda specifies replacement at 30k–45k mile intervals but many owners skip it entirely. Neglected fluid leads to coupling chatter on tight turns and, eventually, rear coupler failure ($1,000–$2,000).
Ask if rear differential / rear coupling fluid has ever been serviced. On AWD models, confirm the service record shows this. A car with 100k miles and no record of this service needs it immediately.
Est. cost: $100–$200 (fluid change) vs. $1,000–$2,000 (coupling replacement)
Source: Mazda service documentation; Mazda CX-5 Forum long-term reports