Yes, if the destination isn't a maintenance base that stocks the part that fails. It's happened to me - 45 minutes into a 1 hour flight they decided to turn around and return to our departure airport. It's very annoying.

The problem is that some failures mean the plan can't fly again until the part is replaced, and sometimes it's cheaper to turn around than to have the plan sit idle until they can get the replacement part out to it along with someone certified to repair it.

Yes, they do. I suggest that you set avherald.com as your homepage for a week, and learn how common air turnbacks and diversions are.

One "silly" reason why minor failures result in flying back to the original airport is sometimes that the original airport is some sort of hub for the airline with plenty of equipment and personnel for maintenance, which makes it cheaper for the airline to repair the plane specifically there compared to another airport. If you follow avherald.com even a little bit, you will notice a lot of incidents result in exactly that.

That would strain the definition of "imperceptible", wouldn't it?

My point is that aircraft break all the time. Once in a while they break in such a way that they need to return to base. This wasn't an MCAS failure.