I've encountered the same issues with oxyclean (or any similar percarbonate cleanser) for long soaks of any type of material, be it corny kegs, vinyl tubing, plastic buckets, whatever. The residue is rock hard and can be removed from the inside of a corny keg with manual scrubbing. "Whitened" plastic tubing just needs to be tossed--there's no salvaging it with vinegar or any other chemical, IMO. I've stopped using it because it just leaves a white film on everything that then requires manual scrubbing to remove. Rinsing alone does not remove it from bottles and kegs.
I suspect the issue is the water profile--mine has a high alkalinity (see Jacksonville, FL). I'd love to hear what Martin B or any other water chem expert has to say about the situation. I'm curious: What is the white residue and why does it occur for some of us and not others?