spartacus 68

Go to a professional body shop. Had a similar issue with an old 2012 A4 Allroad. It’s classed as Platinum Grey 1RR, however will no doubt vary across models. When I spoke to Audi main dealer, it didn't even show up as a code.
Phoned a few body shops and ones that are Audi and Porsche approved and they said it can’t be blended. Entire panel would need to be painted. As it’s matt/satin effect, it’s notoriously difficult to achieve consistent effect with rattle cans. Hope that helps.

Don’t skimp on budget is my advice. I understand you’re looking at B&O, but that needs to dovetail with car model, engine and gearbox and even colour.
B&O was expensive feature, so it’s not likely to be found on poverty spec car. If you find B&O, then it’s bound to have leather, folding mirrors, possibly virtual cockpit would be my experience. Retrofitting anything is expensive, and usually you need VCDS to remove codes, even if plug and play.
I know this is on an Allroad brochure (2017), but it elaborates on the comfort and sound packs. https://autocatalogarchive.com/wp-content/uploads/2017/09/Audi-A4-Allroad-2017-UK.pdf
 
Trim level aside, you want history and lots of it. On cars that have been on long service intervals, personally I’d give them a wide berth. No oil should be in the car for 18k miles.
Be prepared to travel too, once you’ve done your due diligence checks. Additional checks such as Car Vertical which you pay for are useful.

Pretty sure you'll need to undo drive shaft bolt and remove lower balljoint so you can withdraw driveshaft and CV from hub to see. A wobble impact triple square is handy. See videos for Dave Sterl on YouTube. He's done A4, so can't see A3 being different. You'll need a new driveshaft bolt, and torque with wheel off the ground. Bearing wise, F.A.G. every time. Make sure hub face is spotless before fitting. Wire brush attachment on a drill, that sort of thing.

Check exhaust clamps, and flexi (if one is fitted) these can corrode and what you’re smelling is fumes from engine bay. Also auxilliary drive belt, a seized clutch drive pulley, etc.

Speak to Tomas at VAG Technic. Oxfordshire to Dudley is about 1hr 30mins away. They drop performance engines all the time and know their way around S4. I’m sure there’s logical explanation.

Yours will be 2.0 litre 252bhp version if Quattro. Its a chain. Technically speaking there’s three.
If it’s been on long service intervals, get off of that and into oil changes every 8-10k miles.

Laser make conical locking wheel nut extraction sockets. Find one that fits over it, hammer on (needs to be tight) with lump hammer, and extract. Better with extension breaker bar than a power tool. If you’re not confident, just take it to a garage.

It is cam chain. No reason to replace unless you have rattle at start up. Regular oil and filter changes will help keep the engine in good condition, ideally around 8k miles. Ignore long life service regimes, that’s what kills engines.
If for arguments sake it needed replacement chains, guides, sprockets and tensioners, it’s an engine out job. Check out VAG Technic on YouTube. On performance Audi RS and S models, they are constantly stripping them down due to premature fault with rocker arms and needle bearings. 
In terms of maintenance then pretty sure this is 218 is S Tronic 7-speed box. Needs gear oil and filter change every 40k miles. Fuel filter every 20k miles. Once you get to 100k miles, treat rear diff to a fluid change.
Worth investing in VCDS even if you’re not spanner handy, as will pinpoint fault codes, and useful for things like coding battery, etc.
Gave up on main dealers years ago due to ludicrous costs. Find a trusted garage that knows these cars inside out. It’s got air suspension which is pretty robust.

80Nm + 90 degrees for the bearing and carrier triple square bolts. Personally only fit a quality bearing, such as F.A.G. or similar, that will be OE. Make sure the hub face is spotless before torquing up the new bearing and carrier flange. There will be aluminium oxide when the old one is removed, but a wire brush assembly on a drill is perfect.
For the driveshaft bolt, it’s 200Nm plus 180 degrees. Importantly, the axle cannot be on the weight of the vehicle. More details here. 
 
 

To be honest there’s zero value in it. It’s worth more to you than what’s it’s physically worth. I used to have B5 2.5TDI Quattro Sport Avant, and took it to 175k miles. The B5 shape is attractive, especially in avant form. I still search for mine on UK MOT check and sadly its MOT was never renewed after Jan 2024 at 222k miles.
You do see these cars from time to time, especially in southern Europe where they haven’t been ravaged by our winter road salt. The V6 diesel version is fairly bullet proof. 
If it were me, and depending on budget, it would be an interesting project car to completely strip and rebuild. There was something on a different forum with a B5 in Hibiscus Red. However if you’re not spanner savvy, then costs will run away with you. VCDS software is very useful too.
Subframe front and rear would probably need to be dropped, new bushes and powder coated. New Meyle HD multi link suspension all round, probably new dampers, brakes overhauled. Interior wise, should be easier. The matrix dash used to be problematic but can be fixed, plus unsightly scratched interior controls where the rubberised paint has worn off.
Then there’s the small matter of a new paint job. Madness, probably, but if it’s part of the family, keep it.