Hi Viejopatron
What you're describing sounds to me like a function or a malfunction of the suspension bushings that sit between the outer housing and the inner mechanism. On the older SM models, these bushings tend to sag letting the mechanism drop in the housing to the point where the carriage may scrape on the outer shell. On my 1972 SM-9, the screws that hold the mechanism in the housing, also hold the feet onto the unit. Take a look and see if I'm even close.
Sky
We humans go through many computers in our lives, but in their lives, typewriters go through many of us.
In that way, they’re like violins, like ancestral swords. So I use mine with honor and treat them with respect.
I try to leave them in better condition than I met them. I am not their first user, nor will I be their last.
Frederic S. Durbin. (Typewriter mania and the modern writer)