You are correct about the person using the blue substance. It was developed for RR when I was a kid working for them. It’s called Hylomar Blue, I use it also to seal many different things. Metal to metal seal is excellent when petroleum is around. But not too sure it’s the right product for this application as although the product is also good for plastic, it may not be the best for seals as there are natural and synthetic based seals around.the seller was some kind of repair guy(industrial AC, maybe), it was some sealer, brake cleaner couldn't dissolve it.
Idle jets were clogged, whoever cleaned carbs, forgot to clean them.
I've always veered away from using Hylomar Blue on thin elastomer seals as the instructions do not venture into that subject, some people have used it in that area with great success. So using it is more than likely okay for thin elastomer seals, it's definitely okay on metals.I cleaned as much as I could with paper towel, break cleaner didn't help. Hope, diaphragm will not fall apart from this sealer.