Final gear for s2000

[JAP-S2K]

is cryo treated a must? what would you rate it out of 10 for importance?

It's not a must. As it's got it's pro's and con's. It is a good idea as it make the surface harder and less likely to burr on the ends of the teeth. Which in theory does make it slightly stronger, but it also does make the teeth more brittle, which can/is a down fall. It really come's down to one important aspect..... how you drive your car. Nothing will stop breakages if your hard or have an abusive style of driving eg. launches, burnouts, doughnuts, clutch kicking and worse of all, if you let it tramp. Cryo treating could actually have a negative effect under these conditions. Remember that the factory crown and pinions wheels are renouned for snapping.

Are you hard on your car? or was the broken gearbox being unlucky.

[AusS2000]

Which in theory does make it slightly stronger, but it also does make the teeth more brittle

Cryo treating doesn't make material more brittle. It just removes faults int he lattice structure and makes the material more evenly hard, not harder.