I've seen people searching for reviews/experiences with Seiko's USA service center in Saddle River, NJ, so I thought I'd post mine here. Had a great experience with unreasonably quick turnaround.
I sent in an SPB383 that was less than a year old because I was only getting one hour out of the power reserve after taking it off (though it kept great time while wearing it). It was delivered to the office on 12/26, but the maintenance center was closed from Christmas Eve through 1/2. I got an email the afternoon of 1/3 saying it was with a specialist for repair, and they'd be servicing/replacing the whole movement, replacing seals, water/pressure testing it, cleaning it, and testing the new movement.
It was shipped 36 hours later and arrived in Chicago 48 hours after that on 1/6. Four days start to finish once they opened the package, which they did on the very next workday after it was delivered, though they also mentioned that could take up to 7 days after delivery, so I did get somewhat lucky there.
As for function, the bezel feels brand new again with new seals and lubricants, and the watch is running -3 spd after 72 hours without resetting. My previous Seiko's have sped up a little as the movements and lubricants have broken in, so I'll be curious to see if it gets even more accurate over the next month.
Everything was covered under warranty, and they even shipped the watch back in a sweet cushioned zip-up travel box/case that I'll definitely be using in the future. I've read some horror stories and definitely cannot discount those, but figured I'd put my own experience out there too.