1995 300ZX AT N/A @ 194K mi still running smooth should I?

I change the differential oil antifreeze and gearbox oil ever 30,000 miles and the brake fluid once a year or at least every second year. The "on the car fuel injection system cleaners" do a good job. If you have no idling problems or State emission test failure a couple of bottles of techrolene in the gas tank may be no harm. Change the fuel filter as well. Remove the air intake boot and clean the throttle body.

these boxes prefer synthetic oil, i would drain the auto and change the filter , the best replacement oil is redline high temp auto trans fluid, at worst it will last much longer. all the n32 z300 i owned were using this fluid , coolant was 75% distilled water 25% coolant and a bottle of redline water wetter, that dropped the temp about 15 degrees on average, i agree with ngk plugs , i usedn iridium rather than platinum, i used castrol synthetic diff oil , i had no problems over 2 cars and 5 years use.