I thought this would be very helpful to you guys as well.
keep in mind that the 2004 A4s are non return so they are going to be the ones that really want to make sure this is checked. As they have the regulator in the back.
Looks like another maintenance part I will need to get.
So far on my list I have
-spark plugs
-coil packs
-Coolant temp sensor
-o2 sensors
-fuel filter
-vac lines
Can anyone think of anything else I should replace