Audi's continuously variable automatic, fitted to A4 and A6 models through the 2000s — a transmission whose reputation depends almost entirely on whether its fluid was ever changed.
Audi originally specified this transmission's fluid as a lifetime fill — a decision that, in practice, has shortened the life of a great many examples. The steel push-belt and variator mechanism are mechanically sound by design, but depend on fluid condition far more than a conventional automatic does. Changed proactively every 60,000–80,000km regardless of manufacturer guidance, it's a genuinely dependable gearbox.
Not a guarantee, but a pattern seen consistently across owner forums and independent-garage reporting.
Fluid condition on an unserviced example is typically already degraded by this point.
Shudder or hesitation under load becomes a common complaint on unserviced transmissions.
Unserviced examples carry meaningful failure risk; proactively serviced ones commonly exceed this without issue.
Ask directly whether the transmission fluid has ever been changed — many owners were never told it needed it, so a straight 'no' is common and not automatically disqualifying if mileage is still moderate.
A hesitation or shudder when pulling away, especially from cold, is a meaningful warning sign worth walking away from without further inspection.
If buying a car with unknown fluid history, budget for a service immediately — it's inexpensive insurance against a very expensive failure.