Amy, I hate to suggest it. but have you considered testing him for what Chester & the girls have, Giardia? Apparently, it's very hard to detect and takes repeating the test several times to find it. Chester has had several bouts of "dire rear" in the past few months, which I attributed to the Wellness. Of course, now we know what it was all along.

I hope you find the source of his “dire rear” soon.