Being the "guardian" of my own 1945 Brock 54" upright and my stepdaughters smaller: 1900 Broadwood, straight strung, upright, I took a day to fit new damper springs to all the wound base strings. These were "orid" not only practically undamped but also ringing their overtones in sympathy to higher notes!
Big improvement!
But new felts and completing spring renewal throughout is the next step. Hammers still look like new - maybe they are!
I managed to fit the new springs without removing the damper pivot - simply used my "Dremel" to cut out some of the underside of the pivot-flange. Doing this allowed said flange to make a greater angle with the damper post and thus, after removing the spring bush it was easy to pull out the old spring and push in the tail of the new spring.
I used 2mm diameter nylon grass trimmer cord to replace the old spring bush.
A question for the professionals: why use lighter springs for higher notes?
Plainly heavy springs would not be necessary to damp lighter strings, but is there any advantage to the pianist - faster trills perhaps?