Diff oil (standard gear oil) can leak out of the front shafts, and if it leaks enough can blow back on to the downpipes.

I did these on mine a while ago and meant to make a thread on it. I'll stick one together later with part numbers :)

Lubricant dripping onto the catalysts/exhaust is what makes the stink.

No idea how easy it is as a DIY job I've always had it done by a garage. Never said it was difficult though.

Definitely DIYable if you have a decent bench vice. The hardest part is getting the driveshafts out tbh, because you have to pull a lower control arm.

ok , still trying to find the time to have a look at this

did a 500 mile round trip on wednesday and didn't really smell anything so decided the best thing to do is to top up the 2 diff's [ where's the fillers ?] and see if there really HAS been much of a fluid loss ...I have a suitable syringe [ chinese of course ] and if there is little loss leave it pro tem

is that a practical plan , can I get at the fillers ok ? if they are already fullish must be something else one presumes

incidentally , do the front shaft seals have to be pushed in 1.7mm like the rear output shaft one ?

The front shaft seals are a little recessed yes. You can get to the front diff filler with the driver's side wheel off, and ideally the plastic cover which sits over the junction box. It should be checked with the car level, and as usual fluid level is the bottom of the hole.

The torsen filler plug is also on the driver's side on the side of the casing where the torsen is. Can't remember if the exhaust is in the way of this one or not.

You can see them both in this pic:

http://www.corradov8.com/pics/s8/5hp24a.jpg

thanks MJ , I am a bit confused looking at your pretty picture
clearly the front filler does both sides , but the tail shaft comes out of the torsen which is a sort of diff I suppose , but there then has to be a third diff at the rear does there not ? and all of these use 75/90 hypoid I presume

us plymouthians is a bit thick , especially as tempus has flown ![ 65 years since my last latin lesson ]

I've updated the pic. The filler at the front (orange circle) does the front diff, and feeds through a tube behind the torque converter to also do the bearing for the output shaft on the other side.

The filler at the rear (red circle) does the Torsen centre diff.

The rear diff filler is on the side here:

http://www.audiworld.com/tech/pics/misc33-rear_fill.jpg

Yes, they are all 75/90. I recommend Castrol Syntrans for changes but if you're just topping up pretty much anything that grade will do.

Its rare for the rear diff to leak much except at very high mileages. They're usually a little damp around the output flanges but anything worse than than is unusual. That would be unlikely to make its way to the exhaust too.

Yes there is rear diff on the rear axle. Best to stick with OEM oils or equivalents instead of generic 75W90 oil.

I don't know about auto box diff oils but 6 speed manual calls for special oil in gearbox + centre and front diffs. Audi recommends one of Castrols Syntrans oils, I don't remember viscosity but it is GL4+ specification. Regular GL4 is not good enough for high pressure hypoid gears and GL5 wears out bronze bushes and synchromesh gears.

ok , looks like stocking up on some syntrans won't hurt before I go any further the one to GL4+ ; it's available on line here from 123pneus ,1 litre delivered at €15 [ their uk site my tyres does it at £14 ]

I notice that as well as GL4+ it says it is to these VW specs

501.50
GO52 145
GO52 911

any of these sound familiar ?

Thats it ^ G052 911 is the stuff for the 6-speed manual and G052 145 is for the diffs in the Tiptronics. Called 'Syntrans Transaxle 75W-90', although oddly I can't find it on Castrol's site. They may have renamed it?

I first got Syntrans from TPS in favour of the OEM stuff which, frankly, is rubbish. I had an 01E 6-speed which had become nearly unusable on the OEM oil, even after a couple 30K changes. A change to Syntrans and it lasted another 60K so consequently I put it in everything +++

Comma make an equivalent fully synthetic 75/90 too which can be easier to get on the high street than the Castrol.