The turbocharged flat-four behind the WRX STI — genuinely exciting performance from a factory rally-derived platform, with documented ringland and head gasket sensitivity that's closely tied to how the car has actually been driven and tuned.
This engine shares the external head gasket leak tendency found on the naturally aspirated EJ25, with an additional, more serious concern layered on top: piston ringland cracking, most commonly associated with aggressive tuning, ethanol-blend fuel without supporting modifications, or sustained high-boost operation. In factory or conservatively tuned form with a sympathetic driving style, this engine is a known, manageable proposition; pushed hard without supporting upgrades, it's a genuine risk.
Not a guarantee, but a pattern seen consistently across owner forums and independent-garage reporting.
Ringland risk correlates far more strongly with tuning and boost history than with mileage alone.
Head gasket seep symptoms, shared with the naturally aspirated EJ25, may appear within this range on unaddressed examples.
This is the single most important check on any EJ257: ask directly whether the car has been tuned, and get the tuning file and any supporting documentation.
Ask specifically about fuel type used (ethanol blends require supporting modifications) and boost levels relative to factory specification.
Have a specialist perform a compression or leak-down test to check for early ringland-related symptoms before buying a modified example.
Model-specific pages, with notes on how it behaves in that particular car.