My grandson has a '90 NA that he has owned for a few months now. The car belonged to a friend and had sat for 4 years so I had the fuel system drained/refilled prior to sending the car to him. Is it safe to use fuel injector cleaner with a 31 year old (60K miles) Z32? If so, what brand have others used successfully? The car runs fine but an NA needs all the help it can get! Thank you.