If they are stripped or one is just loose, you can probably replace the insert--you might have to contact the manufacturer for a new part. I've had this issue with one of the bolt holes--not the cleat bolts--coming loose in the shoe. The threads weren't stripped, but the effect was the same, since the insert would spin freely in the sole. Many shoes that I've seen have a flap cut or, like Sidis, have a perforated bit for you to cut, under the insole where you can get to the cleat insert hardware. It can be kind of a pain to access the parts, depending on how small your shoes are, but it's probably fixable.