Need a little help please

[Cheddarbob14]

Having an issue with my Oncidium Hilo Firecracker. Plant is doing really well right now but I just noticed a couple dark spots on top side of 1 of the leaves, then realized the bottom side looks almost like a rash. There are maybe a total of 4 other leaves that have similar "stuff" on it, but nowhere near the degree that the 1 pictured has. Any idea what it is? What to do to fix it? I've been fortunate to have not had any issues like this yet, which leaves me clueless on the current situation though!