An advantage of owning typewriters which except for you would likely have fallen into the rubbish bin of history is that any good faith effort you make to get them working is on the side of the angels. The LC Smith Secretarial was basically functional but had a spall in the platen around 1" long and 1/4" wide, maybe 1/16 to 3/32" deep (sorry, metricists) and suggestive of the shape of Manhattan. No harm in trying so I tried filling it with Devcon high strength home epoxy. The first application either shrank or seeped into the inner layers of platen, so when it was almost cured I added enough more to build up the patch beyond the desired final shape. After that got hard enough to sand I sanded it.

I learned why not to use cheap sandpaper (grit comes off rapidly) and also something I partially anticipated, that sanding freehand was not a great idea. For one thing the cured epoxy is a bit harder than the hardened rubber so if you just free sand over the patch you will be sanding valleys into the nearby rubber. I got it close and used the typewriter itself to check the shape - lines of capital H's fill area and you can readily see uneven printing, and it turned out that gradual out of round is not too bad but anything that fells like even a slight ridge under your fingertips is going to cause drop outs.

Is it factory spec? Of course not. But it does move the machine into territory where it works enough to use and the slight irregularity of imprint near the patch is no worse than the general slight irregularity of imprint. It wants a few more items fixed but time for a road test! Review to follow.