O-ring size help please

[Stocker]

How to find the exact size o-ring for my transmission dipstick tube (72 K20)?

The one I removed seems quite new (I paid a shop to replace it a few years ago), but is leaking -- so it may be the wrong one. Comparing by size, it seems to be a #112, which is 11/16" OD x 1/2" ID x 3/32" thick.

It seemed to fit the tube properly, but it was leaking. I have read that some brands are a bit thicker than others even though they are listed as the same size. Unfortunately my local NAPA has no o-rings, and the ones at Ace hardware (my only other choice) look exactly the same size as my old one.

Any help would be appreciated! Thanks...