Just this afternoon having put the roof back up, the passenger window stopped half way up making exactly the same noise the drivers side made 6 months ago when the regulator failed. Fortunately this time I was able to coax the window back up and have sourced a new one from Mazda at half the price Fiat quoted and in stock rather than a 2 week wait with Fiat.
In conversation with Mazda's parts man, he confirmed that water ingress causes internal corrosion and results in regulator failure. My car is coming up to 7 years old, with both regulators failing within 6 months of each other. I had noticed the passenger window going slow over the last few weeks, so if you notice the same It may be worth changing the regulator (part costs £45 from Mazda) before it fails and leaves you with a window you can't close.
My passenger side failed at 22k and 4 1/2 years old. I got both from Mazda at the same time. My spool was also rusty and frayed, so when I fitted the new one, I greased the wire before fitting. Bit old school, but we will see.