Oncidium Twinkle....or is it a leopard? Spotted leaves and burnt tips

[MJG]

This is my Oncidium Twinkle that I bought in a cellophane bag at the Maui airport. I posted a NoID thread for this one a couple of weeks ago and got an answer in record time. In that post I included a picture of how the orchid looked 2 years after I bought it. (Below)

Many years later the orchid looks bad! As you can see, spotted leaves and fried leaf tips. When a new growth starts it looks great, but soon becomes spotted.

I've tested it for cymv and orsv -- negative. I've changed the lighting, cut back on the fertilizer, tried totally eliminating the fertilizer to no avail. I divided it a couple of years ago and the division has the same issues.

Could this be orchid fleck virus or a culture issue? Or??