Gear attached to the motor – part of Sony X-3356-638-1 Motor (Reel R) Assembly. Gear is also compatible with Sony X-3371-429-1 that is actualy a substitute part.
X-3356-638-1 Motor (Reel R) Assy Gear 
X-3356-638-1 Replacement Part
Replacement part was created using a semi-professional 3D printer. Slighty flexible material guarantees silent operation. The part was fully tested.
The part is compatible with following devices:
TCKA2E, TCKA2ES, TCKA2ESU, TCK620, TCK850, TCK850ES, TCRX79ES, TCWR901ES, TCWR99ES.
It also might be part of other device – just check corresponding service manual.
Available in e-shop.