Frister Rossman 300 cog broken?

I have a Frister Rossman 300 inherited from my Mother {RIP}, it works well except doesn't zig zag stitch so I took the top off to oil it and discovered a metal cog was broken, I don't know what it does but assume it's the problem.
Any advice welcome.
Russell, April 2022


done
This guy might be able to offer help if you contact him

https://www.sewingparts.co.uk/frister.html

Erldjh, April 2022