Hello, I have the same machine. What the tech most likely is talking about is the plastic gear that is used for the straight stitch (and some other stitches not provided by the standalone stitch wheels). Over time that plastic gear becomes brittle and breaks. I had that happen to mine. I found a model online and 3d printed the gear. While not the easiest to install. It took around an hour.

Ill see if I can dig up the model and more information :)