The marks in the middle of the gears are normal. They helps move gear oil. Your transmission looks in good shape. I would refresh the bearings and synchrnos. Make sure the bearing don't make noise before you put them on. You will need a press to do this. Link for one here
Here is the transmission kit I used and other parts for my s13 trans:
|1||Transtar|| Transmission Rebuild kit w/ synchrno rings||BK133BWS||$138.77||Link|
|1||Nissan||Main Shaft Nut||32354-E9803||$16.81||Link|
|1||Nissan||Counter Shaft Nut||32236-E9500||$10.16||Link|
|1||Nissan||Gasket for shafter Cover||32516-03U11||21.06||Link|
|2||Nissan||Reverse Lamp Switch Assembly / Overdrive switch (same switch)||32005-21U1B||$30.83||$61.66||Link|
|1||Nissan||Neutral Safety Switch||32006-M8060||$39.50||Link|
|1||Red Line||(MT) 90W Gear Oil - Synthetic Gear Lube||50305||$90.60||Link|
Replacing main and counter shaft nuts are a must. Also you will need to make a special tool to torque the main nut. I welded a 1 15/16 socket onto the old clutch and put a wrench on the main nut. So I was able to torque it down.
Switches go as followed
- Reverse switch (blue - OEM Part# 3200521u1b) Same as overdrive
- Neutral switch (purple- OEM Part# 32006m8060)
- Overdrive switch (red - OEM Part# 3200521u1b ) Same as reverse
- Speed sensor (Indicated with yellow circle)
Anymore questions or pictures needed let me know.