This is at the front a the manual.. the seal that seals in the transmission oil.. the shaft at the FRONT of the gearbox runs through this.

Manual transmissions:

4 speed trans.; with Borg-Warner T10S Transmission
4 speed trans.; with Borg-Warner T10W Transmission
4 speed trans.; with Borg-Warner T10Y Transmission
4 speed trans.; with Borg-Warner T10Z Transmission
4 speed trans.; with GMC Saginaw Transmission
3 speed trans.; with SM326/M15 Transmission

Going off size.. its 

• OD is 44.55 mm
• ID is  31.75 mm