I found it! "Who We Were And What We Meant By It", published in The New Yorker issue of 16 April 1984.
The best, you say?
There was some amazing writing in Keillor's "Mr Blue" column for early Salon (so where can I read that material? long story skipped), and Keillor and I both had our lives changed in Scandinavia, and I first heard shape note singing (which I am now totally into, honored to be friends with shape note composers and hymnbook compilers/editors, wrote my own words for a fugueing tune) on Prairie Home Companion, "Idumea" from the Denson book... but for the past decade I have been unable to even listen to PHC, despite the great music and sound effects, finding it grating and sad. To use a term of my first husband's, it had become a dial-twister.
But this piece seems perfect to me. It's wordy yet also brief. In horse pedigree terms, "by James Thurber out of The Moviegoer" doesn't begin to do it justice. It nods to great humorists of the past, but its limpid profundity is all its own.
But don't take my word for it; go read "Who We Were And What We Meant By It". If you'd like a copy and you know me (this blog is a secret so there's a good chance that you do) I can mail you one, using some of the many commemorative stamps that I also just found ...
You keep saying "found".
Five weeks ago tomorrow there was a fire in the apartment next door, which led to extensive water and smoke damage in our place, not to mention us having to relocate ourselves and our dog, who has been chewing her own flesh as a result, and I've just finished three exhausting days in the salvage company's facility, where I was very happy to discover, in the dampened-then-dried heaps of pre-internet documents, a technically illegal photocopy of this piece that I love so very very much and have so often thought about (especially while I was thousands of miles away from most of my files) despite having forgotten its title.
Did you read this piece the year it came out?
Yes, I believe I did. And unlike some works in my memory, this one upon re-reading still seems as good as I remembered it being.
In the 90s my mother in law started paying for a New Yorker subscription as a gift, under the mistaken impression that because I quoted Wolcott Gibbs' "Theory and Practice..."  from The Years With Ross I was the least bit interested in what the magazine was doing now, now that each writer had their own pencil (cf remark by Dorothy Parker in TYWR), but this was several years before that. (My beloved mother in law has died and I've tried to subscribe to TNY online several times without success: two long stories skipped.)
In fact, looking at this photocopy of these two precious pages  I seem to remember swiping the magazine from whatever I had read it, and making the photocopy, and sneaking the magazine back there. Yes, I used to do things like that all the time .
Digression! & why this piece is tagged "australiana"
One of many wonderful aspects of life in Australia: Aussies love magazines, and love them openly. In the oughts, an industry survey claimed that each copy of a mass market magazine was read by an average of five people. We swapped ours with friends, and then took well-loved stacks of magazines to our doctor's office (universal health care, "bulk billed"), social service office, cafes and churches, and just kept passing them around, enjoying the racy headlines that were the ancestors of clickbait and detailed coverage of "the royals".
It seemed to be generally understood that the point of magazines was to have the hell read out of them; the most obvious example of this was that in most supermarket checkout lines every single person would be engrossed in a magazine; it was 100% socially acceptable to pick up any magazine from the rack and read it until the checker got to your stuff. And anyone who bought a magazine would take the top one even if it was a little battered, because it was about to get more battered and loved-up. I really really miss that.
Thank you, Garrison.
This piece is funny and there's deep wisdom in it and my hat is off to you. Oh, and in the small space at the end of the piece there's a short poem by W. S. Merwin  that I don't understand but that gives me the chills. I'll have to ask Stephanie Strickland for help with it.
Feeling grateful and fortunate. In spite of, in the face of, everything.
 This document is of its time, and I have my own list of guidelines now. But awareness that one could have guidelines, I owe to reading this. The line that I can't get out of my head (and seem to have misquoted to my mother in law, too many times) is from this paragraph:
"Writers always use too damn many adverbs. On one page, recently, I found eleven modifying the word "said": "He said violently, morosely, eloquently," and so on. Editorial theory should probably be that a writer who can't make his context indicate the way his character is talking ought to be in another line of work. Anyway, it is impossible for a character to go through all these emotional states one after the other. Lon Chaney might have been able to do it, but he is dead."
Muttered under my breath, my misquotes would be either, "Lon Chaney could do it, but he is dead," or more succinctly, "Lon Chaney is dead!" No one around me would know why I was muttering, and my (first) mother in law is the only person who has ever asked.
,  You can see a thumbnail of the two precious pages, here. But don't read the abstract, which betrays the humor and structure of the piece, ponderously. Did I mention I have tried to pay them for access, several times now, and yes I filled out the customer comment form ...
[4; Added in Nov 2016] My MOM has just given me a copy of the New Yorker cover with the silhouette of Bob Dylan. She saw it in the office where her RA meds were being infused and asked the staff to make a couple of copies. So maybe I come by this genetically.