I know this has been written about since the start of this site. I believe it's only a problem on 986 & 987 cars. Anyway here's some thoughts and info on the subject.
The stock AOS doesn't do the job on cars that are heavily driven, DE or autocrossed. The harder you drive and more you do to increase cornering (tires, suspension) the worst it gets.
If you just street drive fairly normally you may get away with just replacing the stock AOS and cleaning all the lines and intake runners. Here's testing procedure from Flat 6 for checking the AOS status:
If you are in this category you may just need to realize your car is going to smoke on startup and nothing is seriously wrong with your car. You need to accept that fact and just live with some smoke.
If drive harder or modify your car you will need to install the Porsche Motorsport AOS to control oil in the intake system. This is expensive and difficult to install. You probably will also need a modified or better oil sump - deeper, better baffled oil pan. There are many out there. Bilt Racing has a more recent one.
In addition to this smoking problem early cars have a poorly designed power steering system which Porsche claims is fine, no problem.
Solutions here are:
1) add a power steering line cooler to the front of the car.
2) install a reduction pulley on the belt
3) use RedLine or something like that for power steering fluid
After destroying 3 power steering racks to pump completely; the plastic lines actually melt. Porsche replaced 2 of them($2500+) before I was deemed a RACER and refused warranty repairs anymore. Luckily Hoffman Porsche in East Hartford replaced the 3rd one in my 2006 Cayman RS on their dime. That was before the 4.0 x51 engine. I found that if you just check the power steering fluid after each event and top it off with Porsche/VW/Audi fluid you won't have any problems. It worked for me from 2008 to 2016 when I got a newer 981 which I haven't destroyed yet but I also haven't track this car so maybe it applies to 981's also - not sure.
