You have to post a picture. I have never heard of it before. Sewing machines were made to last a lifetime until some point after 1960. Nylon gears were widely in use by the early 50s, and they can be a weak point decades later. With service and a replacement parts when needed the better models can be used for decades.
The older models still in production stayed all metal until the early 60s. There odd all metal model turn up now and then after this date too, but very few and far between. I once noticed a flat bed 1970s Taiwanese made machine, all metal, straight and zigzag only, but it ran well and was of solid build. It's possible to have replacement gears made, but it just cost too much to be worth it. The other option is to hunt down a parts machine.
Last edited by Mickey2; 01-05-2018 at 11:16 AM.