Using penetrating oil as chrisj mentioned is a really good idea, and the best i have ever used in all my years as a machinist is called AeroKroil made by Kano laboratories. It will work its way into gaps as small as a few millionths of an inch!!!
Also, you didn't mention how many miles are on your valk or the age of your hoses but this would be a good opportunity to change them out if needed. Don't forget to clean out your overflow tank.
Let us know the outcome.
