Polo 9N3: Oil Leak in Transmission

Translated on 03-09-2026, 20:22.

Hello everyone!

My Polo (9N3, 1.4L TDI 3-cylinder, BWB, mileage: 362,000 km) is leaking transmission oil. I have already cleaned the underside of the transmission with brake cleaner and inspected it. According to my inspection, both the oil filler opening and the drain plug are tight.

The transmission oil is leaking from the top. The top of the transmission is also quite oily. Next, I'm going to apply some degreaser thoroughly and carefully steam clean the transmission.

Before I go any further, here's my question:
Is this a typical phenomenon? Do you have any idea where the leak might be – where exactly should I look?

By the way, the transmission has the identification code "JDE" and is a 5-speed manual transmission.

Thank you all!

Translated on 03-09-2026, 20:23.

You don't need a steam cleaner; brake cleaner and compressed air are simpler, just be careful not to pollute the environment.

Translated on 03-09-2026, 20:23.

Rüdi wrote:

You don't need a steam cleaner; brake cleaner and compressed air are simpler, just use them carefully so you don't pollute the environment.

Who has compressed air at home these days?

Despite that, thank you for the information!

Translated on 03-09-2026, 20:24.

Compressed air is more readily available than a steam cleaner; you can also borrow a compressor or know someone who has one.

There aren't many obvious places where there could be a leak, so it's likely the issue is with the wave generator.

Is the transmission possibly overfilled?

Translated on 03-09-2026, 20:26.

Rüdi wrote:

Compressed air is more readily available than a steam jet, and you can also borrow a compressor or know someone who has one.

There aren't many obvious places where there could be a leak, so it's likely the issue is with the wave generator.

Is the transmission possibly overfilled?

Funny, I don't know anyone who owns an air compressor. But almost everyone has a steam cleaner... anyway, I was just at a self-service car wash.

My finding: The transmission oil is leaking from the upper left-hand threaded fitting between the engine and the transmission (a coolant hose is attached to the double fitting).

Do you have any ideas about what I could do? Please don't tell me that the transmission needs to be removed to replace the seal!

There was actually a little too much oil in it (maybe 10ml).

Best regards,

Translated on 03-09-2026, 20:27.

Take a picture of the spot.

Translated on 03-09-2026, 20:27.

Rüdi wrote:

Take a picture of the spot.

Sure!

I've now decided to unscrew the screw in question, apply sealant to the head, and then screw it back in.

Can I do that? Or is there a risk of something shifting or becoming misaligned between the engine and the transmission?

Translated on 03-09-2026, 20:28.

A little more distance would be helpful; you can barely see anything except the screw.

Translated on 03-09-2026, 20:28.

What appears to be oil there is almost certainly not transmission fluid.

Transmission oil is always relatively light in color.

Translated on 03-09-2026, 20:28.

@ Stolley - Could you please highlight what you mean?
The picture shows something more like a sludge of motor oil.
hg
Herbert.

Translated on 03-09-2026, 20:29.

Thank you for your "concern" (or "sympathy").

I'll try to post a more informative photo once I've driven a few kilometers!

Translated on 03-09-2026, 20:30.

stolley wrote:

I'll try to post a more informative photo once I've driven a few kilometers!

Okay, here are some photos. It's not easy to photograph. There's definitely a lot of oil coming from above, which accumulates in the area around the transmission identification plate. However, it also runs down on the other side of the "bell housing," towards the rear.

Translated on 03-09-2026, 20:31.

Hi,

Quote:

Is the transmission possibly overfilled?

... Actually, there was slightly too much oil in it (maybe 10ml).

In my opinion, by doing that, you are indirectly admitting that you have topped up or changed the transmission oil.

Assuming the correct amount of transmission fluid is in the transmission, using the wrong type of transmission fluid can cause it to "foam" and bubble out while driving.

Best regards, Rainer.

Translated on 03-09-2026, 20:33.

dieselschrauber wrote:

...
In my opinion, by doing that, you are indirectly admitting that you have topped up or changed the transmission oil.

Assuming the correct amount of transmission fluid is in the transmission, using the wrong type of transmission fluid can cause it to "foam" and bubble out while driving.

Best regards, Rainer

Hello Rainer,

"Yes, you are generally correct: about half a year ago, I added a little over a liter of oil. The reason was that the transmission sounded strange when driving in low gear. At the same time, I noticed that everything around the transmission was covered in a sticky substance - for me, this was an indication that transmission oil had been leaking out in very small amounts for a long time and had hardened."

The car was parked on a slightly sloping driveway while being filled, which likely explains the minor overfilling.
The oil level should be correct now (at the bottom edge of the fill opening). However, it's still leaking...

What kind of component is installed between the transmission and the engine?

Best regards,
Volker

Translated on 03-09-2026, 20:34.

stolley wrote:

What kind of seal is actually installed between the transmission and the engine?

None at all, because there's nothing there that needs to be sealed.

And are you 100% sure it's transmission fluid? To me, it looks more like a leak from the tandem pump.

Translated on 03-09-2026, 20:35.

I also assume it's a tandem pump. The motor seals against the crankshaft at the front. If the seal fails, the oil will leak out from the bottom. If it leaks out from the top, the clutch will be disengaged.