Hey Radagast, I was going to say OxiClean, but you said you've tried it. Just to make sure, did you try taking a scoop of the powder, putting it in a bucket with water, and letting it soak for 6+ hours? And then washing it? You probably have, but I wanted to mention it.
Since you have put so much effort into it, have you happened to go to a professional cleaner or a dry cleaner and ask for their thoughts? It might be worth paying for a cleaning to "reset" the gi, more or less, and then you can work on maintaining it from there.