Where is the oil coming from?
A gearbox holds only a small amount of oil, and every drop lost matters. First, pinpoint the location: underneath the gearbox, at the driveshaft outputs, around the bell housing, or near the drain plug. A reddish or light-brown stain with a sulphurous smell is typical of gearbox oil.
Likely causes
- Driveshaft output oil seal. At the driveshaft exits: the most common source of leaks, and a straightforward repair.
- Drain or filler plug not tightened properly, or refitted without a new seal.
- Casing gasket between the two halves of the casing or the cover.
- Input shaft seal, on the bell-housing side: oil can then contaminate the clutch and cause it to slip.
- Cracked casing following an impact or a kerb strike.
Can you keep driving?
With just a few drops, yes — but have the level checked promptly: oil can be topped up through the filler plug. With a significant leak, no. A gearbox that has run dry will be noisy afterwards, even once the leak has been repaired.
Repair or replace?
An oil seal or a plug can be changed without removing the gearbox, followed by a top-up with the recommended oil. A cracked casing, or a gearbox that has run dry and become noisy, is another matter — replacement is the right call: a reconditioned gearbox on an exchange basis, tested and warranted for up to 24 months.
