I could only tell you what I have done and it works for me. You can have your own oil analized and see what the results are and then you can make an educated decision on how often to replace you engine oil on your 'Z'. I do not recommend anything on how to maintain your cars. As for anything suspended in the oil, that is what the filter is for. You have the magnetic drain plug and you can also cut the filter open and check it for any metal. The longevity of your oil depends a lot on the driving conditions under which your car is driven.