Face seals are 2 precisely machined metal rings with rubber o-rings backing them. The machined pieces are so precise that when they are put together face to face they can spin on each other without leaking oil. They are the seal that allows the sprocket to spin while the motor is stationary without leaking the carrier oil. Face seals are also used in the under carriage rollers and idlers. If you have an external leak of gear oil on your drive motors the face seals are more than likely bad (thats if you notice the leak). The face seals in the drive motor are very expensive ($200+ last time I bought them) and thats why I want to reuse them. I looked at the parts break down of the drive motor and it looks like I might not even have to mess with the face seals. Now I just need to get the motor apart. The 8 bolts that hold the motor together are rusted in there pretty good. Salt does wonders to metal