Sounds like the rear main seal failed. Usually they last longer than 53k miles but sh!t happens I guess.
You could PM Joe@Zspeed. He is kind of the Z clutch guru around here. I bought a SouthBend stage 2 clutch and lightened flywheel from him.
ZSpeed Performance Nissan Infiniti Specialist 240SX 300ZX 350Z G35 G37 370Z