What is this brown spotting on my miltassia?

[astrid]

Hey folks!

I've had this since September 2014.
It is a Miltassia Charles M Fitch Izumi.

The brown spotting started in a small spot on the leaf above the pseudobulb. Then a few months later, the plant started yellowing slightly. It has barely put out new roots, and now this "rash" of brown spots has spread through the whole plant.

The brown spots are not textured. They are neither raised nor depressed, and completely flush with the leaf. They are on the undersides of the leaf and not on the top of the leaf.

Do you have any ideas about what this might be and if it is treatable?

Should I trash it and buy a new one?

Thanks!