Similar story. To clean my machine I took the bobbin race out of my janome. That involves a few screws and pieces. I put everything in a SAFE PLACE. But when I had put it all back together I couldn't find the bobbin compartment cover, I looked high and low. Couldn't really sew without it. So I trekked my way to the repair store. They tried not to laugh but they didn't have one in stock. But they found one on a used model and sold it to me for $10. Ouch.
About a month later I went into the parts box for a new needle and there it was. Why that part went into the box and nothing else. I will never know.
MaryKatherine