I got a replacement stem from the original EXCELLENT Ebay seller
http://stores.shop.ebay.com/The-New-...__W0QQ_armrsZ1.
I used this stem on a Cinelli Eubios handlebar. This handlebar is 26.0mm in diameter. The Motus stem is supposed to work with both 26.0 and 25.4. The stem's clamp radius seem to fit a 26.0 perfectly, but just like yours, the spacers don't completely fill in the space.
When I clamp this onto my handlebars, both the front triangular metal spacer and the rear rubber spacer have plenty of wiggle room. Like you, I debated on whether to clamp it so the front spacer was tight, leaving the rear rubber spacer with wiggle room, or clamp it so the rear was tight, and the front has wiggle room. I even tried making an additional spaceer cut from an old inner tube. But since it's still rubber, once you tighten the bolt, any faulty stress is still going to manifest itself.
I finally decided to clamp it even, making sure there was an equal amount of space front and rear. The spacers might as well not even be there. Hopefully, this equal clamping pressure will be the safest. Since my original post, I've been keeping any eye on it and there are no signs of cracks.
I'd be interested so see how this fits on a 25.4 bar.
I was trying to get ahold of a Salsa SUL quill stem with the removable faceplate, but that too is a problem unit and I believe it has been recalled. Weird because the SUL stand for Stiff Upper Lip. Instead of a flat mating surface or spacers, it has a lip which was specifically designed to strengthen it.
In the end, I think the smartest thing to do is just bite the bullet and get a Nitto stem and live without a detachable faceplate.