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