My Dura Ace 7400 7 speed cassette "rain" bike, my Saint Tropez has been my go to steed through many seasonal changes and the ups and downs of my fitness or lack of fitness over the years. Currently I run a 105 SC rear derailleur with the 13-25 7 speed unglide cassette. I can't remember the mileage on this cassette, it might have been a used one I got off of eBay. I had an issue with the derailleur hanger on the dropout being out of parallel with the rear wheel and reset it as strait as I could using my Park derailleur hanger tool. All is well except for a single cog - the 5th one (from high to low or big to small if you know what I mean). It is klunking in a not very nice way and it also requires an overshift both in the middle chainring and the big chainring in order to make a clean shift. I plan to scrub the cassette today before my ride and will flip this problem cog then report back later today if it makes any difference at all.

Regards & am eager to hear if others have flipped individual cogs for increased life and precision.

Hmm, not really. The third smallest, or third biggest?

I wonder if one of the spacers is the wrong thickness, throwing off the shifting. If flipping the cog doesn't work, Loose Screws has NOS Uniglide cogs in 15, 16, 17, 18, 21, etc: Loose Screws Bicycle Small Parts Classic and Modern Cycling -- Since 1992!

Though unlikely, that 3rd-smallest cog might have an integral spacer to one side of the cog, and which would preclude flipping it. There were certain of the smallest unthreaded cog sizes that were offered in both spaced and un-spaced versions.
Or I might be confusing some of these cog features with those from Shimano's 7s Uniglide freewheels.

I picked up a uniglide cassette from one of our esteemed forum members and, after I put in onto a bike, I found that the 3rd cog down (the 21t) just wouldn't hold the chain. All sorts of issues, skipping and the like.

I took the cluster apart to inspect. I could not visually determine any "issue" with that cog. While I might have flipped it, I had a nos cog on hand, so I swapped it out. Absolutely no problem now. I still cannot see anything on the "bad" cog that would cause the problem. Go figure.

ymmv, of course.

Update: I flipped the problem cog and it is behaving now. My drivetrain cleaning took place before I went riding causing me to not pay attention upon reassembly and I ended up assembling the cassette with a smaller (higher gear) cog out of sequence. Something like cog #3 changed positions with cog#4. I had wonky shifting throughout the ride but it was such a beautiful day and my fitness is coming back so I was happy knowing that whatever mechanical mayhem has been created, it is most likely sortable.

I've done it. Flipped my 4th cog on a 7 speed cassette after I got a new chain and it was skipping like crazy. Works fine now.

I now remember that I am using a well used cassette that I got fro eBay. Normally the cog number engraving faces outward. The cogs #'s 3,4,5,6 & 7 can be flipped so the engraving is not visible any more. I believe this may be a good way to get more thousands of miles out of a well worn Uniglide cassette.