She called saying "they're saying 'the lug nut broke'"; I was thinking (and asking) "how is that possible (it can't possibly be a defective lug nut)?" 10 minutes later "the stud is broken"; 5 minutes later "they [Costco] admitted to breaking it".
The resolution was to have a local shop replace the lug stud and get reimbursed for the repair cost: $125 (the part might have cost $2)!
I chalk this episode up to them hiring warm bodies lacking any mechanical experience or aptitude (to the extent of not being aware of "righty tighty, lefty-loosey") and handing them an impact wrench.
But there's a reason that r/justrolledintotheshop talks about "uggaduggas" as a torque spec - to make fun of the people who just let an impact driver pound away at things like lug nuts. Cross threaded? Screw it, more uggaduggas! It'll snap when someone takes it off? Not My Problem!
Oddly enough, it's not always righty tighty. I rode motorcycles that had axles that were the opposite (so normal rotation would tighten them), and it was well known on the forums that if you let a shop just go at it, they'd try to loosen it, tighten it, smash the spacer, and your wheel bearings would then fail in short order. I always either watched the shop take my wheels off, or just took the wheels off myself and took them in to get the rubber replaced (alarmingly frequently - I was riding a lot).
So history argues in favor of it being their fault. In fairness, they were apologetic and never tried to absolve themselves of responsibility.
Regarding "Costco should have had zero problems replacing a broken stud on the spot", I wish it were so (would have saved a bit of hassle), but which expert person at Costco is going to be capable of doing this? They seemed to have shop nearby that they farmed such work out to, but this problem occurred on a Sunday...
That said... I'd have wanted to pop into the shop and personally inspect the remaining studs to make sure they weren't on the brink of failure as well.
It's also not uncommon for garages to under or over torque fasteners because they're in a hurry. My friend had his power steering pump come off the engine block while he was driving because the garage didn't bother torquing it properly after replacing it.
>Every decade or so, I try a fast oil change place, usually when I'm in a hurry, and it sells me on changing my own oil for the next decade, because it's either obscenely overpriced, they screw up my car somehow, or both.
The last time I resorted to having someone else change the oil in my car, because I was in a place where I couldn't DIY and didn't have time to go to a relative's place to do so, I used an actual garage and not a quick-change place, thinking they'd do a better job, I provided the oil, and they managed to overfill it by more than a quart.
The people that take jobs like these are simply incompetent; if they were smart, they'd be doing other jobs.
Because you like your car...
Every decade or so, I try a fast oil change place, usually when I'm in a hurry, and it sells me on changing my own oil for the next decade, because it's either obscenely overpriced, they screw up my car somehow, or both.
Last time I took vehicles in for oil changes, it cost nearly $200 for my truck (I know it takes a lot of oil, but ffs...), and for the car, they didn't get the airbox back together properly, so I had a nice post-air-filter leak. They even left the bolt they couldn't get lined up sitting in the windshield air inlet tray - because they'd not lined the filter box up right. And, they forgot a crush washer on the drain plug, so I had a dinner plate sized oil puddle under the car in the morning. Sorry, I see no point in paying someone to screw my vehicles up like that.