My old house in Lynnwood has a leaky roof. Do I need to replace the whole roof, or just do a partial re-roofing?
It's hard to say. If the leak has been there a long time -- sometimes a minor leak will do a lot more damage than a big leak because it may go unnoticed for years -- the damage might warrant a compelte re-roof, but usually, it's a question of repairing what is underneath the leak itself.
More research from the Internet: