Thanks for stopping by at hamvention - you mention Mendelsons, were they back this year? I know last year they did not come. I didn’t have much time in the flea market so maybe I missed them this year.
As for the ! that’s weird, I checked hamlib code and it shouldn’t be injecting the ! either. This may be similar to behavior in Arduino problem with gPredict and rotctld
You might try running rotctld in verbose mode and pasting some of the responses there. In the meantime I’ll poke @azisi and @csete for their thoughts.