Well, they do have an idea of who they want to be owned by, don't they?
I can't say for sure what Sydney's past is, as you can't. You may be dealing with the fallout from something that happened years ago. Example: My Fred was hurt by adolescent boys, mostly. Just the sound of a boy's voice is enough to set him off. He (mostly) trusts my husband now, though Ron does get bitten more frequently, where I have enough trust with Fred to let him preen my eyelashes and he lays upside down on his back on top of my head while I"m sitting at the computer.
What I would do, if I were you, is to sit by his open cage/stand and just pay no attention to him, reading, or doing some sort of handwork type thing. Don't look at him. Then, perhaps, read out loud to him. My birds LOVE to be read to. Once again, don't look at him. Perhaps eat something wonderful! Do this for a LONG time...weeks? Months? Make sure any talking is low and soothing. Let him get curious as to what you're doing. I find anything that takes concentration like embroidery is good, because they have to run over and get everything tangled up <G>
Let him approach you. He's naturally curious. He'll eventually figure out you're harmless. He'll make the overtures in time. But you can't rush it.
When he does come over, don't pounce on him or try to move quickly to pet him or anything. Just let him be with you. As he gets more comfortable, he'll probably shove his head into your hand, if for no other reason than to get what you've got in your hands...one reason why food is better than embroidery!
This could take years. It could take days. But let HIM make the moves...let him decide to trust you. Let him be the boss, at least in this little way.
(and wear the reading glasses, if it seems to help!)