I have used Seafoam, but not for the carb seals. On the motorcycle, I used it for winter fuel storage. It is both a gasoline stabilizer, and an anti-moisture additive. I found it works well for both purposes.
I have also used it in my car as an engine / gas system cleaner. It worked very well, especially when injected directly into the intake system through an evap. port.
Bottom line, to the extent that I have used Seafoam for any of its claimed purposes, it has done the job. Several people I know swear by it for cleaning out residue and stuck sludge from the oil system when changing the oil.
Also, I will say that since I used it this winter, a pesky leak at the carb bowl seal has gone away. Could be coincidence, or not.
k_enn