Have you dunked it yet?
Before taking it apart, I make it a habit to remove the lens elements, then soak the shutter assembly in naptha (lighter fluid) for a while. Working it after it's been in the naptha for a while often frees up old lubes that prevented the mechanism from working. Most often, the shutter will not require relubing, but sometimes a second soak in graphite powder dissolved in naptha will help, if it sticks. Try to remove as much graphite as possible, or be prepared to pull the elements frequently to clean the lens surfaces that are contained by the shutter.
You may also be disappointed in the coverage on a 4X5, but give it a try.
Jo