Bernina 830. I've had this machine since the early 80's and have hardly used it as it has never

Question

I've had this machine since the early 80's and have hardly used it as it has never worked properly. my latest issue is that the zigzag selector will not turn back to straight stitch.

A Bernina 830 sewing machine was given to me and had not been used in quite some time. I threaded it and started it up to see if it still worked and everything was running smoothly, then it suddenly stopped, but the light still worked. Manually moving the needle also still worked smoothly. It suddenly began to work then stopped again. I'm going to clean it and oil it, but I was wondering if there may be a more serious problem? Thanks for your help.