CW's bloodwork was all within or very close to normal limits except for his glucose level. Cats tend to get very high glucose levels when they are stressed though, and Clueless was very stressed when they took blood from him. Neither The Real Vet nor I believe he is really showing signs of diabetes. Lipase and creatinine were both up marginally, but these aren't diagnostic of anything, and could both just be stress induced.
CW was spiking a fever all weekend, and evidenced some pain on kidney palpation. We're still waiting for the results of the kidney tests to come back. Kidney failure can look like this, but again The Real Vet and I both doubt that this is the problem (we just can't rule it out yet).
Best guess is that this is some sort of viral/bacterial infection. We have him on Flagyl right now, which is a very good antibiotic to use on cats with gastro-intestinal disorders. Why Clueless should be sick when neither of the other two cats has caught this is a bit of a mystery though.