There are all kinds of carb and brake cleaners. The MSDS for Gumout carb cleaner shows MEK, so that's probably what did it in. Viton doesn't play well with MEK. I try to pick cleaners that don't have the nasty stuff in them. I found a brake cleaner that's glow engine compatible and used it to flush silicone parts without a problem. Usually the ingredients are right on the can so you can check at the store.