cannot seem to pull off the Brake Booster vacuum hose (to treat with seafoam).

Hello, First, I have to say that I do not encourage you to do the seafoam treatment, I'm just telling you how to get the vacuum line off. You can either separate the vacuum hose from the elbow that goes into the brake booster, or you can pull straight out on the elbow to remove it from the brake booster. Easy in both cases, unless the rubber is hardened. I recommend you get a new rubber grommet for the vacuum line if it is so much trouble to remove. This isn't surely needed, but better to have it on hand, and you will not spend a fortune on it.