The only time I've seen a milky substance in carb bowls was when there was water in them. We used to keep a glass jar in the shop and when we'd drain the carbs you could see if any water was in the gas. It was usually in globules rolling around on the bottom (water being heavier than gasoline). I worked on a snowblower recently that had water in the carb. I could tell as when I removed the bowl drain, the liquid that came out just beaded up on my shop rag- whereas gasoline immediately soaks right into it.
I imagine that if there was a sizable amount of water in the bowls, the bike would have run poorly (the main jet would be pulling water, not gas), so if it didn't run badly I can't say for sure it was water that they found... MEK (MethylEthylKetone) is the only thing I know of that will dissolve Kreem lining. Does anyone know if there is MEK in Seafoam? If so, how much?
<edit> According to one website, the MSDS for Seafoam says:
Seafoam ingredients:
1. PALE OIL 4229 40-60% = A base or process oil refined until its color = yellow.
2. NAPHTHA 20 25-35% Powerful solvent, common in all good injector cleaners. (Zippo juice!)
3. IPA 125 10-20% = Isopropyl Alcohol (Useless in gas, since it already has tons.)
OK, so no MEK.. Looks like that disproves that theory...