I ONLY use a Korky flapper for all generic replacements, which yours is. You do NOT really believe that Borg Warner actually made either the toilet or the flush valve, do you? The toilet is a rebrand from another manufacturer, and the flush valve is a generic part they bought from whoever gave them the best price.
I actually wonder if the bulk flapper he is talking about buying at Ace isn't the bulk-packaged Korky 52P "economy" vinyl flapper.
I can't imagine, however, why the Korky Plus wouldn't work.
Is there any reason that people who have problems finding the "right" flapper couldn't just replace the flush valve with the Korky universal flush valve to which the Korky Plus would surely fit? It's not like the flush valve is expensive.
EDIT: I was actually at an Ace in New York City today, and was checking to see if they carried the Korky 92BP MaxFlush flapper (formerly called the Korky "Lo Pro" for lowboy toilets), which I think will help the flush of my hideously-functioning AS 2014 Galleria until the building replaces it, which is taking a while. With its styrofoam insert, the 92BP appears to have been designed to make lowboys like mine flush better by emptying the tank fully. Of course they didn't have it so I ordered it online. They did have a huge selection of Korky flappers, including a whole bunch that came in Ace packaging but were embossed as LaVelle or Korky. Indeed, they even sell the Korky Plus in an Ace box for a dollar more than they sell the regular Korky Plus. ("Ace Korky Plus" it says -- $5.99. It's right next to the blister-packed Korky Plus for $4.99. Go figure.) In any event, I saw what I think is the box the poster was referring to -- loose-packed, bagged blue-green Vinyl flappers in a bin that says something like "Ace Economy Flapper" -- so I inspected one. Yep, embossed with the LaVelle Korky name, part 52P, Made in USA. So that is indeed the one with which the poster had success on his Borg-Warner generic toilet. Of course, I would be inclined to follow HJ's advice that a good regular Korky flapper should work well on any generic toilet.
As an aside, I also want to thank this forum once again for giving me the knowledge and inspiration to tackle so many (simple) plumbing problems myself recently. Now that I am so much more informed, through the forum and by actually doing the projects, paying attention to how things are designed to work, do work, and work together, and experimenting with various settings to see how they affect performance, I could see that the toilet that I despise in my apartment in the city really had not been adjusted properly by the maintenance folks, despite numerous visits. That Galleria is a marvel of over-engineering: it has a variable diverter, and a trip lever that sits in a different position with the cover off than with the cover on, thus requiring you to use more chain links to set the chain slack than would appear when installing the flapper with the cover, obviously, off. And on and on. With its large horizontal internal tank, small differences in the water level mean big differences in the water volume within the tank. With some tweaking by me and a temporary replacement with an adjustable Korky Plus flapper until the 92BP arrives, at least I don't have to hold the button down for the entire flush process, and the flush is measurably-better. Of course, it's still an exciting, lengthy and unpredictable ride with every flush as the water whirls for 30 seconds before revealing whether those 3 sheets of toilet paper are going to actually go down, or whether I have to reach for the plunger, but it was fun to have the ability to tinker with it and at least to get it to work as it was probably designed to work. And I really appreciate all the accumulated wisdom on the forum from Terry, HJ and all the other contributors.