Need 1956 speedo cluster rebuilding advice

[lts70]

I'm about to jump into a speedometer rebuild for a 1956 3100. I changed the speedometer cable that ran from the turbo 350 transmission and although the needle moves now, it is very erratic and has a fairly loud knocking noise from inside the cluster. I was hoping for advice from those who have encountered a problem similar to this. Or any other advice in shining one of these old clusters up. thhings to do or not to do.

I have rebuilt many 67 – 72 instrument clusters. But I have so many spares that when something doesn't work I just swap parts. Don't have the luxury here only one cluster to work with
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