Yup, what everyone else has said...I use K&N (#HP-1008) even with a Stillen oil cooler. Seals properly and works well. It's slightly bigger in diameter compared to the OEM one.
If you have the inclination to do your own oil change, the Z is quite easy to learn on. The oil filter and drain plug are close to each other, so drain pan placement is good with minimal mess. The only tedious part is removing the 16 bolts that hold the under tray in place. Just find and follow AK's DIY and it's a piece of cake. You'll need to buy a copper crush washer for the drain plug (never reuse an old one).
