Awhile back I noticed that the seals on the rear differential were starting to slightly seep some fluid. I was told instead of spending money to repair it I just needed to make sure that I maintained the proper fluid level by filling it every so often.

This will be the first time that I will check the level/fill it if necessary. My question is should I replace all the fluid while im at it or is that unnecessary?
Ive heard that it is lifetime fluid but I know that some people have replaced it.

Car has close to 120k on it

 

Wouldnt hurt to replace it, I did and many do. Not really cheap though it needs full synthetic (75w-90 I believe), and it isnt a fun project either, one of the worst smells you will ever smell. I am in the same boat, mine is leaking from a the cv shaft seal, but it leaks so slowly that you only have to top it off very sledomly. http://www.audiworld.com/tech/misc33.shtml theres the writeup, I had to have a shop break the fill nut loose cause it was on too tight. You cant really check the level, but if memory serves me right you just fill it until it starts to spill out of the fill hole, but check that writeup im sure it says.

 

As a side note, if you don't have a suction gun you can also refill it with some vacuum line and an air compressor.

 

-Thanks for the replies. I was planning on getting a suction gun...not sure how much they cost. I do have an air compressor, how exactly do you fill it with that and a vacume hose?

 

Go to carquest and they have this thing for like 4 bux that you screw right onto the bottle and press a button up and down to push it into a tube, I thought it worked great. Its a little slower but cheaper than a gun.

 

It's really simple, and pretty fast as well, it's the way I did it on my Z and the way I'm planning on doing it on my A4. Takes about 10-15 seconds to empty the container.

Explaining it makes it sound more complicated than it is, it is really very easy:

You need two pieces of vacuum line (or really any generic rubber line), one piece will go from the fluid bottle to the diff filler hole, the other will go from the fluid bottle to the air compressor.

You will stick both hoses in the top of the fluid bottle and you will need something to seal the top once the hoses are in (I used the original cap for the bottle and drilled out holes for the vacuum lines--sounds a little silly, but I did this on my Redline bottle and because the cap fits all the bottles, you only need to do it once and screw the cap onto the new bottles once you empty the previous one--in fact I still have the cap and am going to use it for the A4 too).

The hose going to the diff filler hole needs to be fully submerged in the fluid, at the bottom of the bottle, the hose going to the air compressor needs to be above the fluid level.

Then you simply pressurize the hose going to your air compressor and about 10 seconds later all the fluid is in your diff.

Then screw off the cap, put it on the next bottle and there you go.

So like I said it sounds involved writing this all out, but it only takes about 5 minutes to get the hose/cap ready and 10-15 seconds to empty each bottle.