10000% this!
I'll add that Apple Authorized Service Providers generally have the flexibility to sell you a replacement part as a "stocking" part, which is to say that they do not require your defective part back. Though the parts cost is higher and almost always not worth it unless you just want the extra part to keep in stock (hence, "stocking").
Why do you need to keep the fan assembly? Isn't the entire point of this exercise to return your machine to working order? I get wanting to be in control over your own repair and over the defective part, but I'd just pay the cost to return your computer to working condition, especially if a $359 repair bill is all it is. That's honestly the best news when it comes to fixing a Mac Pro that, at the absolute minimum, was $6000 before taxes.
Tried calling the local repair shop here that's authorized and they are stonewalling too.
My main line of reasoning are the fans are working 100% properly, just the sensor is bad. I'd like poke it with a sharp stick, at worst, I have a backup set of fans for a very expensive computer and at best I'd have a fully functioning assembly.
Fans have already had issues once, I'd rather have the option on the table to fix it myself. What the ever living **** is the point a modular computer that effectively is a locked box? I don't think I'm wrong here, it's absolute madness Apple will not under any circumstance sell me the part and just let me repair it myself and absolutely criminal that they require me to return the faulty part in order to get service.
Secondly, this isn't primary work computer, it's a personal machine that I use for work sometimes, and side projects so I have a bit more flexibility with it.
/edit: called a shop in another town, awaiting quote but sounds like they'll play ball. It's a bit of a trek but I could easily fold it into visiting my friends who live there. Again, I can't believe how terrible Apple is on this: It's fan assembly on a modular computer. I'm lucky I live in a major city. The Mac Pro 2019 isn't exactly easily mailed.
Transporting a 40 pound machine isn't exactly easy for everyone either. It's not an issue for me but this could be a massive headache if you lived in a small town / remote area, and/or needed an assist moving the thing. Apple requires a two person lift when handling the Mac Pro (I saw a sticker on it when they gave it back). They might have a leg to stand on if this was under warranty but it isn't.
It's been years since I've dealt with Apple repairs, but they make a machine to make us right to repair crowd happy only to shoot themselves in the foot. I don't get it.