Truth bracket is corroding on crank window

I'm afraid I don't know what screws were used for your particular window. My suggestion would be to remove one of the existing screws--one of the ones in better condition, of course--and take it to a local hardware store to allow them to match up the precise size.

I'm not certain from your question if you also needed a new operator. If so, I'd be happy to look into it, but I'll need a clear picture of the complete mechanism. Seeing it removed would be ideal, but I understand if that's not something you want to tackle just yet, given its current condition. At the very least we need to see as much of it as possible to ensure that no important details are obscured or missing.