Silly question time, was this particular bike been wrecked/on the deck?
Reason I ask is, I have been dealing with very similar issues. And the usual suspects haven't produced any 'It's fixed!' results that I thought they would have.
Turns out, I had two different issues contributing. First, was the bottom left fork leg 'lightly' ground down on the very bottom. Ground metal was making the pinch, well, not pinch.
The other issue was a bit more insidious. The front fender was not riveted to fork/fender brace. The fender literally could/would flop/flutter around. Anytime I pulled onto my parking pad, I go over a hump, that produced an audible/feelable knock. I chased everything I could reasonably think of. It wasn't until yesterday that I was going into one of many 'search party' adventures, that I realized there was something amiss. I took the fender completely off, bolted the Murph's forkbrace back on, that came on the bike when I bought it, and lo-and-behold, the bike was transformed! Gone was the skating/marble/wandering/hinge feel, to something much more akin to a solid performing bike. Perfect? No, this bike is old, in age and design. But much more to what I thought I would be getting myself into.
Not that I advocate such activities, but on the way into work today, I held triple digits the entire time on the expressway.
This has been the most frustrating bike I have ever dealt with. But it has so much of what I want, that I felt compelled to keep at it.