It seems only a VW dealer can give you the code--they look it up from a database, based on both the car's DIN # and a part number on the radio itself. You can take the car to a car audio shop and they will remove the radio for you and then provide the necessary part numbers. Call the dealership and along with the VIN number they will provide you with the code. Once you have the code there are several steps you have to take to input the code.
VOLKSWAGEN PASSAT 1998-ON 5x112
http://www.tobio.info/passat/howtos/passat_air_filter.html This is for the 2.8L V6 30V
You can find the wiring diagram for the stereo of a 1998 Volkswagen Passat in the service manual. It shows what each color wire is used to connect each component and where the wire is routed.
in the fuse panel
On a 1998 Volkswagen Passat the starter is located front of the transmission housing. To replace the starter the car needs to be raised so the starter can be reached from underneath the car.
inside air filter housing
the radio code is on the back of the radio. take the radio out and you can see it.
How do I unlock my 1998 I 30 radio reset
The reset code is on the back of the radio,
Go see the VW dealer. They have special tools.
10w30 for sure. Ask the guys at Checker or Auto Zone to look up what type of filter you need.
The transmission is serviced with lifetime fluid and does not have a dipstick. The fluid can be changed by the dealership with a special tool.