We haven't done the flash test. I read on the DM forum that 1 in 4 dogs test negative but do have DM. That seems pretty high to me. I'm going to ask the vet about it, though, and see if she has any experience with it.
I'm curious about the other issues you mention that present the same symptoms. I'd be interested in them. I've done a lot of reading and the things I have found don't seem to quite fit.
Sadie the GSD ~ RIP 4/6/09