Martha,
My wife's Bernina 930 came to her about 12 years ago from my cousins estate. My cousin had bought it new in the late 80s I think. I do not think it was ever serviced or cleaned. I know it hadn't been from the time my wife got it until I took the plates off around the bobbin area about 3 months ago. That machine was packed with lint and thread, and yet it showed no signs of quitting. A modern Singer would have choked up and stalled long before it got as bad as the Bernina.
I cleaned it out and oiled everything metal that moved. Now it works quiet again. My wife has discovered just how good that machine is and wants to start picking up attachments and accessories she doesn't have for it. It's worth it.
Joe