If it has already been thoroughly cleaned, you can try putting a small drop of machine oil on each side of the vibrator, on the portion where the vibrator slides, and working it through.

It could be that the ribbon vibrator might for some reason be pulled forward a little bit--like a nonworking ribbon reverse pulling the ribbon taut enough to bend the vibrator a little forward.  What you might do is to set the ribbon control for "RED," and push a type bar near to the top.  Push back on the top or upper part of the ribbon vibrator on both sides, and see if that helps.

Hi Typngon

​Looking at my SM9, there are two springs that work to pull the ribbon vibrator down to home position. The heavier spring is connected between the left spool frame and I believe it's called the universal bar. The other lighter spring is under the machine just next to the right rear foot and is connected between the rear frame rail and the ribbon lift shaft.

The other thing I'd check is make sure all the linkages between the U-bar, ribbon lift shaft, ribbon lift actuator arm (bell crank) and the vibrator itself are moving freely and don't interfere with any part of the frame. Hope this gives you something to work with. All the best,

​Sky