There is a tradeline on my credit report from Exxon from 1989. It isn't mine. It was my dads. I tried to get it removed a while back (pre-CN) "that's before I found Creditnet." He and I have the same name except he is junior and me the III. This card was closed a long time ago with a great CL and low usage. There is one 30 day late on it and that's it. Well it was never removed and it appears on all three of my reports. I figured I would leave it alone since (1) it's closed, (2) the tradeline dates back almost 15 years and (3) I have a new Exxon/Mobile card; which also now appears on my reports as positive. So when I get ready to dump Capitol One or Orchard, I will NOT have to worry about it being my oldest tradeline. I can go ahead and give them the boot even though Capitol is really my oldest tradeline of a year ago. One of the "Positive" items that appears on my reports says "oldest account is 14 years 6 months" or something like that so I know it's that Exxon tradeline because I have nothing even close to that on there after that.
You're doing the right thing--leave it alone! Don't even worry about the late payment. If you tried to have it removed you might lose the tradeline, and then your score would actually go down.