1.I too have used the Amsoil EA15K50 oil filter on many of my oil changes Bob but,I have got in the habit of changing my oil and filter every six months or before/after every track event I attend. I will do my oil/filter changes since it is part of my general maintenance schedule for my Z.You can continue to use the Amsoil EA15K50 oil filter safely I recommend not changing it every 15K miles. 2.I use the Amsoil EA15K50 oil filter and harm should not occur or the internals in the oil filter should not come apart as long as you are changing the oil filter on time. I would change it out at least every six months or use Nissan's oil change interval.I would never trust changing any oil filter every 15K miles regardless of what the manufacturer says. 3.You can use the Amsoil Signature Series and change it up to once every year I was told by the Amsoil reps at the last SEMA convention I attended if I'm not using my Z at a track event then it's changed before and after. Amsoil recommends their Signature Series because it contains the most ester properties in it compared to their OE and XL Series motor oil lines but,you can use OE,XL,or Signature Series because they all have an amount of ester in them which is what the VQ37HR requires. 4.To combat carbon build up/ deposits I recommend changing your oil on time as Nissan's recommends every 3750 miles or every six months whatever occurs first. Amsoil recommended their 5W30 Signature Series to me since it will provide the best engine protection on or off the track. The Amsoil EA15K50 or WIX oil filters will both provide excellent filtration and always change your oil filter every oil change. I did read that the Genuine Nissan oil filter does have the best design for the VQ37HR engine. 5.People looking to research what motor oil and oil filters would be best for them to use for how they use their Nissan 370Z check out
www.bobistheoilguy.com you will find a lot of information there.