[morzh]

O this is the way I made the tires for the tuning caps.
I had no luck finding something that looks like what it should look like and works.

I also am not sure if the tire should engage when the knob is pushed in, in order to the dial to be able to rotate freely otherwise for fast tuning, or stay engaged all the time.

All grommets that look similar and could be cur in hald to resemble the original are either too thick, or too thin, or have the inner hole diameter too large.
I liteerally spent hours on the web.

Here's what I came up with eventually.

I bought rubber bushings ID=7mm OD=16mm  Height =8mm, made by PATIKIL, sold on Amazon. This is the only size that is close enough.
The original tire (dried up) is ID 8mm OD 16mm Height 5mm. 

So then I took the bushings to a grinding wheel and just took 1mm off first. Then used sandpaper to round the edges. 
This proved too much. When the screw holding the knob was tightened, the bushing pressed onto the dial so much the latter could barely be turned.
So I took another 1.5mm, again, took some of the walls at an angle to make a cone, and then smoother the edges with sandpaper.

Works fine. One is engaged all tthe time but rotates almost freely; the other two need to be lightly pressed upon, and this is my understanding this is how it should be in order to be able to fast-tune.


This is the bushing
   

This is the machined bushing.
   

This is the knob and the tire assembled.
   

And the whole thing