I agree with Sleddgracer,
Don't just seal, give the water a path to escape or it will find its way in.
Before you get too crazy with roof repairs make sure that it is leaking
I have icicles in my bus right now. Not from leaking but from it being 25F outside and I am running the propane heater in the bus. Propane burning dumps a bunch of moisture in the air. The moist air hits he cold metal and condenses then freezes making little ice trails and icicles.
When it is a bit warmer it simply rains when I run the propane heater.