About 5 years ago I broke my frame. A whole bunch of life changes happened and there was no urgency to replace it. But I have been watching marketplace - I'm in a remote rural area so there's very little lugged steel frame activity.
Last week an old Colnago Sport came up for a very reasonable price and I bought it:
Saddle, stem, bars and rear wheel from my old bike, other bits came with the "new" one.
I'm nearly 60 and wasn't really expecting to ride it - it's more a nostalgia thing. But I went for a short test ride and it feels great. I may actually spend some time on it.
And don't worry - I'm not under any delusion that I have a great Italian icon - I know the "Sport" model is Colnago in brand only. But for my purposes, it's perfect.
I used it on an old bed frame cuz I hated the rust stains on my sheets and pillows. It worked out great. The white cures black and acts as a primer. So you can paint over it, but it won't ruin the current paint.
It'll just give you a solid black patina that's resistant to further rusting. You can paint over it or just leave it.
If you want to touch up the paint maybe look into some ... essentially it's nail polish (that's what we use at the shop.) I really don't suggest spray paint unless you know what you're doing. But nail polish or touch up paint is really easy to apply.