Part number 1000-139-068 is a ring-snap for Velvet Drive 72 series transmissions. See the 72C series for more.
Item 707 on the Velvet Drive 5000V V-drive parts diagram (P-3 Input shaft). 6 per transmission.
Also comes in: 2002-410-001 gasket and seal kit and 2001-410-002 clutch kit.
See it on the parts diagram