RustyJames 

I truly appreciate the input from everyone.

I took the derailleur off to have a look. One of the jockey wheels is sloppy and the tension spring for those cogs isn’t providing enough tension on the chain. There are additional locating holes for the pointy end of the tension spring in case my situation arises (thx Tullio!) but getting it all back together as it was previously was a challenge so I need to have a think. Both derailleurs may get retired to the “special parts” box and I suspect I’ll be doing a lot of searching for early 70s Japanese mechs. Suntour Cyclones look (kind of) appropriate….

Erzulis Boat 

I have a Campagnolo SR rear derailleur that looks basically new, but was totally funky on the shifts. After much frustration, I discovered that one of the parallelogram pivot pins would back out occasionally and it was just enough to allow a slight collapse/twist of the assembly.

Another thing, as we age we tend to want to go bigger on the rear and start running things either borderline or to the point of poor and incorrect function.

I would make sure that everything checks out mechanically in the entire system to include the shifters/cable and then perhaps get back into the then designed gear range of the component. I would go "smaller" (and closer) in the rear. The 10 tooth difference in the front taxes those vintage rear derailleurs to a pretty large degree already, not to mention the the stuff going down in the back room. Give the vintage drivetrain a chance!

Chinghis

Omigosh, I'm not a real C&V'er, I guess, as I've never seen that Legnano badge before. Crap, I'd give you lots of money just for that. It's beautiful.

Sorry, no input on the original RD question, I just really like that badge.

obrentharris 

I agree with all of the above points about clean pivots, good spring tension, and smooth-running pulleys. The early version steel pulleys like you have are adjustable and their little balls benefit from a bit of fresh grease.

I've had very good luck getting Record derailleurs to shift a 14/28 freewheel, but there is a definite technique to shifting a Record or Nuovo Record derailleur, especially with Regina or other straight-tooth cogs. When shifting to a larger cog you slightly overshift, then almost instantly trim back to where the chair runs smoothly. This becomes second nature after a few dozen shifts.
Brent

Velo Mule

It depends on what skills you have, what your willing to put into the part and how much value it may have sentimental or otherwise.

I have been watching Paul Brodie videos. He has the skills to repair damn near any bike part (human powered or engine powered). The Nukeproof hub that he repaired was, a lot of work. I don't know how many people in this world that would want to do that. I would have tossed it in the garbage. I think that Mr. Brodie has mastered his machining skills enough that doing these repairs is just fun for him. And it doesn't hurt that guys like me will subscribe to his channel, which brings a little income to the Paul and Mitch show.

On the other end of the spectrum, would be someone that buys a new or better condition old part and saves the time and effort for something else. Maybe riding.

RustyJames 

As awkward as I was phrasing it in my original post, this is the sort of info I was looking for. I often come back to cars since they have occupied a HUGE part of my life but shifting an old Alfa Romeo quickly from 1st to 2nd gets you a nasty crunch. You learn to live with it.

Those of us who own the bikes love the badge too! FWIW - one of those badges can cost quite a few lira.

The Golden Boy 

You win!

86? Supposedly some weird, obscure restaurant code for 1 restaurant? Right. Not.

Deep Six? How does that make any sense?

How about a phrase literally MILLIONS of GIs were/are familiar with....

It's DX. Direct Exchange. Get rid of the bad one and replace with a new one. Often used as just "get rid of."