I have a 2009 6MT Coupe that just turned 50K miles.

Other than some P0300 codes occasionally, there’s nothing else wrong with it that I can find.

What do you recommend for service interval at 50K/12yrs? Is there anything I should check before Infiniti does?

 

Check how old your tires are, they degrade significantly past the 5 year mark. Tread depth isn't what glues you to the road, the chemical makeup of the rubber does and that's what degrades with time.

Since you're throwing a random misfire code it's probably time for spark plugs, inspect the well tubes for any oil seepage, you may need new valve covers if they're leaking into the well tubes.

Brake fluid, you're probably still on the stock brakes but the fluid will be FULLY saturated with moisture and needs to be flushed out.

Transmission and differential are on a 30k mile service, if you haven't done the gear oil in them then it's time. No need for anything fancy, your JK transmission just needs the correct viscosity unless you do ever track the car in which case you should use Redline oil.

Power steering fluid is probably getting contaminated, every time you do an oil change you should use one of those bottle adapter gear oil pumps (the kind that works like a hand soap dispenser) and use it to pump the fluid out of the power steering fluid reservoir then fill it back up with fresh fluid. After 3-4 fluid exchanges like that over the next year or so you will have sparkly clean power steering fluid again.

The G37 still has a few corrosion problem areas on the undercarriage, next time it's on a lift use some rust reformer spray on anything obviously starting to get a little rusty that's part of the subframe bracing. Pay particular to the "W" brace on the rear of the car, it's the same one used on the G35, it and the front has all the same problem areas as the G35. The rear subframe on the V36 platform switched to STEEL instead of aluminum so check it over thoroughly as well.

Your rear diff bushing is probably worn out, see if there's any indication it shat it's fluid out, 50k miles is usually about all they're good for, replace with a polyurethane bushing if it's been leaking.

That's basically it, fluids and rust.

Also, for the future, yes we do have a subforum here on G35DRIVER.COM specifically for the G37 cars however it's rarely used and it was made before the sister site MYG37.COM was up and running. You'll have a lot better luck asking vehicle-specific questions over at MYG37 because it's dedicated for your exact car.