Oncidium with damaged leaves

[Jugyjoy]

Hi everybody,

Would anyone be able to diagnose the damage on the leaves of this oncidium. The plant has two pseudobulbs. One with the leaves pretty much clean, but the other with extensive lesions. The lessons are round, pale and have a white center. Elsewhere there is some rust coloured damage of irregular shape. Please see the attached photos.

I have never seen anything like this and wonder if this could be sun/cold damage, fungal infection or pest. I should add that the surface of the damaged leaves is a little slimy.

Many thanks for your help!