How long do Oncidium Heaven Scent live?

[gardengirl13]

I honestly can't remember when I got this plant, probably 15 years ago. The last couple years it's just been.... blah. The flower spikes don't get very long/tall and only have a few flowers on them, the one a few weeks ago was so far buried in the plant/roots that the flower looked like it was just it and it's little stem and nothing else. I haven't lost a single leaf or bulb in probably 8 years (aside from one leaf that I just lost 6 weeks ago that was burned when I first moved into this house 6 years ago) the others I'm losing them a lot over the last month. The roots seem to be well above the mix so I water up where they are. The new growth seems not quite accordion but bent in various places along the stem (so it's kind of accordion looking but in length not width like I've seen on other plants) and sometimes just doesn't want to open. It's been in the same window (bright, picture, east facing) in almost the exact same spot for 6 years, watering/fert is the same, everyone just got repotted last year and are all settling in very nicely, but for some reason this guy is just going down hill. (I posted a few months ago about damage to another orchid and after giving him a bath every 5 days or so for a couple weeks he's doing much better! The damaged leaves are even looking ok, not great but good enough to help support the plant) so besides this oncidium and a Iwga Apple Blossom and my cocleata who all give me grief from time to time everyone else is doing very well. It's not like I don't know how to care for it, I'm just wondering if I should kind of butcher it and cut out all the old stuff that's been hanging around for the last 10 years or just leave it and see what happens? Is it nearing the end of it's life? I've looked around a bit and can't find longevity for oncidiums, or if they normally just keep going and going growing new bulbs? But like I said this guy has never had old leaves and bulbs go yellow/brown and die back in at least 8 years maybe even longer, it just likes to hold on to every leaf it's ever grown! Is that normal? I want it to thrive and grow better spikes to enjoy it more.