You know those tuning control-dial cord interfaces that get slippy. I had one last night, and it looked rather too polished. So I figured that a little more friction may be needed, so I used a round needle file to gently roughen the surface where the dial cord touches. This one looks like a pulley. After getting the dial cord back on, it seems to work better. I'll see how well it holds up over time.

I also changed out the rubber grommets that mount the tuning cap. The old ones let it sag too much, making some trouble for the dial cord.

You are right on about the tuning shaft or other surface becoming too burnished over time and needing to be roughened. Friction is our friend here.

What some others have done at certain points where friction was needed along the dial cord was to dissolve a small amount of rosin in a little alcohol and paint it on the cord. After it dries the cord "gets a grip!"

There was (or is) a product called Non-Slip that was sold maybe by Walsco for this purpose. I have some of it but haven't opened it for years. If I recall correctly, it's a powder.

Over at ARF I have read a thread about using Elmer's spray adhesive to help give a dial cord some "tack". Just spray some in a cup then paint it on the cord. I think I'm going to try this on my "new" Zenith clock radio this weekend.