B8 S4 Rear Diff Leak

[F40GT346]

I have a 61 plate B8 S4 Avant with sports diff. Its just come back from its first MOT and the garage reported a slight oil leak on the rear diff. Its outside of warranty by around 4 months. Its not dripping but there is an oil stain. Has anyone else had the same problem, is it a problem that needs immediate attention or is keeping an eye on it to see if it gets anyworse (e.g. oil spots in the drive) a reasonable approach? I am assuming it will be a fairly expensive job just to replace diff seals.

Views welcome.

[F40GT346]

lemonslap said:

Big thread here on it:

http://www.audizine.com/forum/showthread.php/41632...

Thanks for bringing this to my attention. Seems like it is a common issue on 2011 cars. Not sure from this thread if the conclusion was a sports diff seal issue or grease from the half shaft joints.

This is the first time the car has been up on a ramp outside of an Audi dealer. Its 4 months out of warranty but seems like a good case to have a discussion with my local dealer.

There is no noise from the diff and I haven't seen oil on the ground but I have noticed an unusual smell when getting out of the car after some hard driving - could this be the grease / oil on the exhaust as seen in some of the pics in this thread?

[F40GT346]

lemonslap said:

Have you checked the oil level in the diff to see if any oil has been lost?

No, beyond my scope of car maintenance. Will take it in to a dealer for a look. The garage that did the MOT said that it was a "patch" and no visible drips so will hope its OK for now. It drives fine and nothing has changed - other than the MOT!

[F40GT346]

My S4 is now back from my local Audi Centre. Initial diagnosis was that it needed diff seals replacing on both sides. I spoke to Audi UK as the car was 2 days out of warranty when this was spotted. Audi UK spoke to the dealer to discuss what contributions they may or may not make. I then got a call from the Audi Centre Engineer who explained that the diff seals were fine, not leaking and that the "sweating" was from the CV joint gators and that this is considered a service item and nothing needed doing to mine at present - just a quick clean up. This explanation tallies with the thread posted above, some owners had the diff replaced, others the oil seals and others the CV boot was identified as the cause.

One the one hand I am glad the diff is OK. On the other hand I cant help but be suspicious of why the initial diagnosis changed - was it really that a more experienced engineer looked at it and was aware of the issue (the Audi centre's explanation) or was it that they were being asked to contribute to the cost? If they hadnt been asked to contribute by Audi UK would they have replaced the diff seals at my cost anyway - the parts were ordered in and the car kept longer to do the job.

Will continue to enjoy the S4 now its back though. Great car.