Why S15 gearbox is sucks?
They have fitted wrong size circlip likely break off for mild tuned, it will leave 4th floating but I'm not going putting full of details so here links you could read extra information *LINK* .
My friend who does gearbox recon/rebuilded, I'll paid him 1,500 V$ to rebuild and improve it.
Here I bought from online...
Competition Clutch's Stage 3 clutch - 350 V$.
competition Clutch's Lightened Flywheel - 300 V$.
She is waiting fresh flywheel, clutch and gearbox arrive...