I'm in IT hardware, and I work on a lot of printers. I see the "rebuilding" problem first hand every day. In order for the rebuilding business to be profitable, you have to put as little money into the cores as possible. So parts that are close enough go back into production. On a printer, that means the reman part doesn't last as long because the bearings or the wear surfaces are already pre-worn. Or that new, cheap toner cartridge that prints nice and dark on the first page ends up leaking all over the place and ruining the fuser because it is dumping too much toner.... argh. Keeps me in business though...
I have bought my share of remanned car parts, and have seen the same thing. The better brands have better quality control, but I have seen where the cores have been worn out from too many cycles of rebuilding. The older and greater volume cars seem to be most affected. Especially on places where there are slide contacts or pivot contacts, like the notch where the pads slide into. (Or mounting ears on things like alternators.) Sometimes the difference is just a little extra slop in the pedal, or the difference between a noisy pad and not. Or they might use oversized seals to bridge the gap in a worn bore. It works and is probably safe, but not as tight as a new piece.
So on your own car, you can rebuild the cores the one or two times that is the life of the car. But when you buy a remanned part, you don't know how many times it has gone through the process. The thing could be 10 cycles old, and expose design problems that you'd never see on a normal car. Parts that might literally have a million miles on them.
