Subaru STI: Rear Wheel Arch and Sill Rust (JDM Imports)

Japanese domestic market WRX imports entering Australia from the 1990s onwards are susceptible to rust in the rear wheel arches, inner sills, and floor pan due to Australia's wetter climate relative to Japan's drier regions. Factory underseal is thin and cracks with age, allowing salt and moisture ingress. The rear inner arch seams and the sill drain channels are the primary rust initiation points. Structural sill rust is a roadworthy failure and can compromise body rigidity.

• Bubbling paint on rear wheel arches
• Rust visible at bottom of door sills
• Soft or spongy floor pan when pressing underfoot
• Musty smell inside cabin
• Visible rust holes or perforation in wheel arch lips

1. 1

   Inspect rear wheel arch lips and inner seams closely - push along the inner arch seam and feel for softness indicating rust through.

2. 2

   Check door sill ends and lower sill edges with a screwdriver (light probing).

3. 3

   Look under the carpet at the floor pan corners.

4. 4

   Inspect the spare wheel well for standing water or rust.

5. 5

   If a workshop inspection is possible: Check jacking points for structural integrity.

Parts involved: Body corrosion.

≈A$740 to ≈A$4,140 at independent workshop rates, shown as an approximate guide in Australian dollars. That is for this job on its own, not for the car.

An estimate, converted to Australian dollars, for the repair as normally carried out. What a specific car costs depends on which part has failed and what it damaged on the way — treat this as the floor for a negotiation, not a quote.

• “Has the car ever had any rust repairs done?”
• “How long has the car been in Australia and where was it kept (coastal/inland)?”
• “Has the underbody ever been treated or rust-proofed?”
• “Is there any bubbling paint around the wheel arches?”

The failure described above is documented in published sources — owner forums, technical service bulletins, recall notices and workshop write-ups — held in our fault database. The inspection instructions and the cost estimate are KickTyres’ own interpretation of them, and it is a starting point for an inspection rather than a manufacturer statement.