I worked parts counters at various CSK stores from 2003 to about 2009 (I believe?) the O'Reilly days were a sign for me to go ahead and attempt my second exit. But there was no ill will there, it was a great job and such a great simple time in my life.
I have similar stories and experiences. Each store I worked in had it's own personality, customer base, and varying proportions of commercial customers. I, too, had many days of explaining the various changes and iterations of small-block GM engines over the years... often times done with more gentle charity than the offending party warranted. And this was all before there was much of a "meme culture" around this stuff- you just had to look young, be a woman, or not speak the same first language as the other guy; and they were off to the races.
The day-to-day drags I don't remember too much of... the eye rolls and sighs from people you were trying to help, the infamous "Ford Mercury", the Cherokee (or was it Grand Cherokee?) that we couldn't seem to get the right parts for, delicate situations with people who were stranded (or stranded themselves by dismantling) in your parking lot, people that expected you to work on their cars for free, shoplifters, turning away refunds on parts used to "guess and check" repairs, gang members, ignorant people, tweakers, thieving coworkers, janitorial work... I kind of just let all that go.
The good day-to-day stuff I DO remember... my favorite customers who brought me fun projects to try and dig up in old cross-reference catalogs whenever I had some extra time, or the good commercial accounts that I liked sending good business to. Jim Rome in the morning and Dodger baseball on KLAC at night. Learning enough Spanish to fluently and convincingly sell almost any car part, but fall apart if they asked me how my night was going. And of course the long days and nights with my coworkers... just chatting and living while holding down that counter or loading up the shelves.
I put myself through college doing that job. By the time I was graduating I had moved on from my initial career ambitions- so I kept working as a service writer after, at least for a couple years before I was badgered by a friend (for a whole year) to move on. It's crazy to look back and realize that I've worked in the auto industry (now automotive adjacent) my entire adult life... I had applied to that CSK job the week of my 18th birthday. Now whenever we're in an auto parts store or a tire shop my wife tells me that the smell brings her back... the smell of those stores reminds her of me and us, back when her and I were figuring this all out and just having a good time. Now we've got a house, a family, stressful (but rewarding) careers, and a whole heap of responsibilities. But we also still have our 01 XJ, and her 95 YJ... and even picked up some broken VWs along the way. And we also still have each other, and all those great memories.
As it turns out, the whole was indeed much greater than the sum of all those parts. Thanks for the trip down memory lane, Cam. We all need it once in awhile.