Yipeee, I'm the proud owner of a cream and green vintage beauty!
The machine was owned by a lady in her eighties, who bought it new; she was the one and only user. She sew some clothing for herself and did some mending, but overall I believe it was very, very lightly used considering the pristine condition of the machine.
When I first tried it, it was grunting like an old bear. I though: there something wrong. Also, the speed was very slow, even with the pedal down. But it was stitching and the stiches were beautiful! I was puzzled. I asked the lady when it was oiled for the last time: she told me she didn't know she has to oiled it. Ok, maybe the poor thing is just thirsty. That would explain the grunting. I opened it; no rust, no crack on the gears, everything was looking fine. The lady was asking 100$ for it, and it was the first Bernina listed in my area in a whole year for less than 300$. Also she kept it for me 4 days before I was able to go try it, even if she add a lot of interest, and that was nice of her. For no rational reason I was sure it would be fine, so I took a chance and bought it.
This morning I cleaned it a bit and oiled it. I also discovered that there was a button to reduce the speed and the button was at low! I put it back to normal, tried the machine: purring like a kitten and stitching beautifully. What a nice machine! I already finished two kid's pant with it and I'm in love.
Thank again ladies for your good advice.