Oncidium Sharry Baby with brown spots

[Ashmelon]

Hi all,

I recently purchased one of my first Oncidiums (sharry baby), and I've noticed that there is a spot that is slightly mushy on the bottom. There is also a leaf that has a few black spots surrounded by a lighter brown spot that keeps getting larger. (See pictures). Not sure what I should do.

I can't see the roots either, so I'm relying on the pseudobulbs to tell me if it's underwatered. Are they looking healthy and not too shrivelled?

Any advice is truly appreciated.