Nice little score there. I'd certainly put down the cash for that.
There's always going to be one more last one. ;-)
The flat spring is supposed to dampen the action to make typing quieter and more even. Here's a photo of what it should look like. Brother machines have a similar device but it is made from wire.
Yes, it looked just like this (i still keep it in the typewriter case).But in this machine made everything worse: faint impression, hard keyboard...