MajorCommonFluid Leaks

Subaru STI: 5-Speed Gearbox Rear Extension Housing Oil Seal Leak (GC/GF MT)

5-Speed Gearbox Rear Extension Housing Oil Seal Leak (GC/GF MT) is a common fluid leaks fault on the Subaru STI on the 1994–2000 cars, and we rate it major. Putting it right costs $280 to $750 at New Zealand independent workshop rates. Below is what goes wrong, the symptoms to notice on a test drive, where to look, and what to ask the seller before you hand over any money. It is one of 32 documented faults on the Subaru STI.

Vehicle: Subaru STI
Years: 1994–2000
Fuel: petrol
Gearbox: manual
System: Fluid Leaks

This page covers the Subaru STI as a model. Some faults only affect particular engines or build years — enter a plate below to narrow the list to one car.

All Subaru STI faults32 documented faults on this model

What you are looking at

No photograph available

We do not hold a verified photograph for this fault yet. We would rather show none than show a picture of something else.

What goes wrong

The rear output shaft seal on the GC/GF 5-speed manual transmission is a documented wear item that weeps or drips gear oil from around 100,000 km. The seal sits at the junction of the gearbox tail housing and rear propshaft flange, exposed to sustained heat cycling and vibration. JDM imports that have spent years in NZ or AU conditions frequently arrive with an active leak from this point. Neglected leaks drop the gearbox oil level low enough to cause synchro and bearing damage, making it a lower-cost item with significant consequences if ignored.

What you would notice

Gear oil drips on the ground under the centre of the car, behind the gearbox
Oily residue or staining on the underside of the gearbox tail housing
Burning oil smell from underside after a run
Low gearbox oil level on inspection

How to check it

Where to look. Rear extension housing of the 5-speed manual gearbox, propshaft output flange seal

From underneath the car, inspect the rear of the gearbox tail housing and the area around the rear propshaft output flange for gear oil residue, fresh staining, or dried deposits. Check the ground beneath where the car usually parks for oily spots.

What it costs to put right

$280 to $750 at New Zealand independent workshop rates. That is for this job on its own, not for the car.

An estimate, in NZD, 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.

Ask the seller

“When was the gearbox oil last changed, and what level was it at?”
“Has any gear oil leak been identified or repaired on this car?”

Now check the Subaru STI you are actually looking at

Everything above is true of the model, and it is free. What it does not tell you is whether THIS car has been looked after: its odometer history and whether the reading has ever gone backwards, whether there is still money owing on it, whether it has been reported stolen, how many owners it has had and what it is really worth today. That comes from the official records for that plate. Enter the plate for the free details, or get the full history and a market valuation from $13.49.

Not sure what you would be paying for? See what a full KickTyres check includes.

Where this comes from

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.

Subaru STI buyer questions

Is 5-speed gearbox rear extension housing oil seal leak (gc/gf mt) serious on a Subaru STI?

We rate it major and common on the Subaru STI. The rear output shaft seal on the GC/GF 5-speed manual transmission is a documented wear item that weeps or drips gear oil from around 100,000 km. The seal sits at the junction of the gearbox tail housing and rear propshaft flange, exposed to sustained heat cycling and vibration. JDM imports that have spent years in NZ or AU conditions frequently arrive with an active leak from this point. Neglected leaks drop the gearbox oil level low enough to cause synchro and bearing damage, making it a lower-cost item with significant consequences if ignored.

How much does it cost to fix on a Subaru STI?

$280 to $750 at New Zealand independent workshop rates. That figure is for this job on its own. A car showing the symptoms on this page is usually worth either walking away from or negotiating down by at least the repair figure.

Which Subaru STI years are affected?

Our research records this fault on the 1994–2000 Subaru STI. Build dates move around, especially on imported cars, so treat the range as the years to look hardest at rather than a guarantee either way. The official records tell you the exact build and first registration date for the car in front of you.