Hi all,
so, I just wanted to give a little update. Thanks to everyone for the advice you gave. I ended up removing that pseudobulb with a sterilized scalpel removing from the pot and soil and and giving the plant a good soak in a hydrogen peroxide solution for a wee bit. The rot hadnt spread all the way down the bulb which gave me hope it might be able to be saved.
And lo-and-behold this is it now.
I have been holding off posting a pic until I was confident enough it was going to survive (lest I ended up with egg on my face), but now its got some nice green roots reaching into its new potting mix and there's a second shoot form the other backbulb I am relaxed about sharing this update.
I was definitely given the confidence to attempt this from everyone's advice - cheers!!!!