The case has been repaired with a piano hinge, an old repair. The front flap of the case is a weak point and many show up online with this bit missing or broken. Otherwise the case looks fine and hardly any rust on the hinges. Amazing how small it really is.
When taking it out of the case, it looks like all the mechanics of the machine really fill the available space of the box. Not a lot of space left (just a small gap for the spare ribbon tin).
With this one I was quite lucky, all the defects and damages were minor and easily fixed. It now types quite nicely again. The left Fig-shift key got badly bent at some time, this makes the shift-lock a bit harder but I'm not going to try to bend anything back. It had a ribbon that still had good ink, but was rather worn and torn with holes. This is now replaced with a new ribbon (nylon). When the kids found out that such things as purple ribbons existed (and that it would then print in purple!) it absolutely had to get a purple ribbon. So of course it has.
This is a late model, serial number 673841. From the available lists online this would be from 1934; one year when relatively many were produced.
It came without any manual, so the online resources came to the rescue with two different scans. These really were useful; I'll admit the locking of the 'shift' before folding was not immediately obvious to me (but did figure it out). One that I'd never have found without the manual is that there actually is a carriage lock too. Many thanks to the kind people that scanned and uploaded these. And very impressed with the amount of functionality that Corona engineered into such a compact machine.
These manuals were all for 1920-ies models and showed the knobs to be fastened+loosened to change ribbon travel. With some reading up, the various models become clear with the 'Special' models introduced in 1929. This by the way matches the little spike in production volume. The 'Special' still have the knobs to change ribbon travel direction. This machine has the ribbon looping through a wire 'S'. When the ribbon is pulled taut at its end of travel, it pulls the wire 'S' sideways and switches the travel. It can also be done manually by pushing the squarish push-rods in front. Ingenious.
With some trawling around, I'm guessing that around 1934 another product refresh was launched with an automatic ribbon reversing mechanism. This would match the little spike in production numbers.
Coincidentally I now found (and bought) a manual for the Corona 3 'automatic' from an antique book seller. This booklet has a printing date of 1937 and it labels the machine as an 'automatic'. The pictures and instructions do indeed show the automatic ribbon reversing mechanism. (Will scan.)
So now a Corona 3 'automatic' it is.