You wouldn't be the first to get a 'rebuilt' Floz unit with a bad coupler. ZZP cut him off on the replacement couplers some time ago (back in '02) and he was in the hurt locker for awhile. It seems he shipped a few with bad ones before he found another source.
A coupler SHOULD go 75-100k with the average driver on a stock pulley. The lifetime goes down proportionally with the weight of your foot and the diameter of your pulley drop.
For instance, my ZZP coupler is pushing 3 years old. It'* just starting to rattle now. That'* an early death, but you can guess which car it'* in.
With two L67'* in the house, I keep a spare handy.