Hello, had my '04 G35x for 2 years now, put about 40k (133k total) and running strong!! Looking for some parts that I can't seem to find if anyone can help.
1. Rear shock mounting plate (in the wheelwell)
2. Bolt size and pitch to replace mounting studs/bolts for said mount above.

Local Infiniti dealer was no help since they never called me back. Nobody could a sweet my question on where to get the part. Thank you!

 

This is from a few months ago but I came upon it while trying to figure out the same problem with my 2003.

1. Rear shock mounting plate: You can find this at parts.infinitiusa.com . Put in your car's info then go to group G > Rear Suspension > Shock Absorber. The part you want is lookup code 55322. For my 2003 it was 5322-AL500. You can have an Infiniti or Nissan dealership order it.

2. Bolt size and pitch: I used a class 10.9 M8-1.25 bolt 30mm in length. Anything 30mm - 40mm long should be OK as long as it is fully threaded. In some places it can be hard to find hardened metric bolts so you can try a 5/16"-18 grade 8 bolt about 1.25" long. Shouldn't matter that it's not metric if you're replacing the bolt and nut.

Replacing the bolt: To replace the bolt properly you should remove the rear seat and weld in the new bolts (try not to set your insulation on fire). If that's a bit daunting I've seen people post about reaching through the center hole and JB welding the bolts in place.

Gasket: The parts diagram shows a gasket that goes between the bracket and the wheel well. I'm assuming this is for vibration purposes. I didn't want to pay $40 each for them so just cut some out of 1/16" grade 60A rubber.

 

I ended up welding the plate back together and running two bolts through the wheel well (instead of a welded stud)with locking but and washer. Not the prettiest, but the kyb shocks keep the car planted well. Thanks for the replay! ( Better late than never)