Yep. Send the GW to whoever is reporting, or in this case, the OC. For the address, I'd recommend using an old statement first. If not available, then start with the address listed on your CR. You can sometimes find this info of the myFICO reports. If not, then try pulling your CR directly from the CRA.
If they help you, absolutely your scores could increase. The increase would depend on the severity of the baddie, the age of the baddie, and the number of baddies you'd have remaining.
Warning: some OCs have been known to delete at the sight of a GW. If this TL is older than your avg. age (AAoA), the OC summarily deleting it could harm your scores, even with the presence of a CO. On the flip side, your report will look better for it. If younger than your avg. age, expect a decent increase.
Also, some OCs have been known to place a "dispute" with each CRA. If they do, your score could actually bump. However, once the dispute clears, then your score could revert back.
Finally, TU is reading as a good account. Some OCs/CAs have been known to be a pain and report equally across all 3. In this case, there's always the chance they would make TU look bad.
If I had to make a decision, I would look at the age of the TL. If not too old in relation to the other TLs, I would GW without hesitation.
