What is the best way to fix Audi A4 oil leaks?

Honestly man, I have been exactly where you are with my old B8 and its a total rite of passage. If you are seeing oil near the firewall and smelling that nasty burning scent at stoplights, its almost certainly dripping right onto the turbo or the exhaust manifold. First things first, stop guessing and throwing parts at it. Grab a few cans of Brakeleen Non-Chlorinated Brake Cleaner and go to town on that gunked-up area. You need a clean slate or you will just blow through that 400 bucks on stuff you dont actually need. Once everything is dry, start the car and watch the vacuum pump. Its that round component sitting right on the back of the cylinder head near the firewall. Shops usually try to sell you a whole new pump for a few hundred, but in my experience, you can usually just grab an RKX Vacuum Pump Rebuild Kit for Audi 2.0T for a fraction of the cost. Those internal seals get brittle over the years and let oil weep straight down the back of the block. If that pump looks dry, then look at the PCV system on top of the engine. If the VW Audi OEM PCV Valve 06H103495AE is failing, it builds up internal crankcase pressure and literally forces oil out of the weakest seals. Its a super common failure point that people overlook while chasing gaskets. Start with the cleaning and the PCV, then move to the vacuum pump seals. Youll save a ton of money doing it that way.

To add to the point above: be extremely cautious about jumping straight to the valve cover gasket without checking your crankcase pressure first. On these B8 models, a failing PCV valve is often the root cause of the other leaks because it creates too much pressure and forces oil out of the weakest seals. I would suggest comparing these three common failure points before you spend that 400 bucks:

• PCV Valve (Oil Separator): I suggest sticking with Genuine Audi PCV Valve Oil Separator 06H103495AK. Pros: it protects your rear main seal from blowing out, which is a multi-thousand dollar repair. Cons: it is pricey for a plastic part and might not be the actual leak source, just the catalyst.
• Upper Timing Cover: Look at the Elring Klinger Upper Timing Cover Gasket Set. Pros: relatively cheap and much easier to access than the lower cover. Cons: the plastic covers can warp over time, so sometimes a new gasket alone wont fix it if the cover itself is bent.
• Oil Filter Housing Gasket: If the oil is pooling in the valley of the engine, this is your culprit. Pros: stops the heavy dripping. Cons: labor intensive because you usually have to pull the intake manifold to get a clean angle at it. Definitely grab a telescopic mirror and check the back of the cylinder head. If you see fresh oil right below the vacuum pump, it confirms that top-rear area is the issue. I'd use Gunk Original Engine Degreaser Heavy Duty to get a clean slate first. Just be careful not to soak the electrical connectors while you're cleaning everything off...

@Reply #2 - good point! Tbh, I was super happy when I finally stopped my leak.

• grab a cheap mirror It works well for seeing that firewall gap without guessing.