68-72 Nova owners come on in..

[Lynn]

Sounds like the sliders aren't sliding.
You do have two options (well, three if you count selling it to Marlin as an option).

Convert to mono leaf. Much smoother. But you will sacrifice some traction control. The multileaf springs actually provide some damping action, kind of like an old friction shock (yeah, I am that old - but in fairness, only the Brits were using those after I was born). Problem is, after time, they provide more damping (and less spring) than you want, and you get the rough ride.

Refurbish your springs with new sliders. When I did mine I lubed all of the sliders with a bit of antisieze. Rear moves up and down almost as easily as if it had coil springs.

I am putting some old heavy duty Koni adjustables on the back of mine to make up for the decrease in damping. It also means if I want serious traction, the slapper bars go on.