How to do maintenance on a harmonica.
Authors that produce several videos:
specific model - Marine Band
Notes on specific models:
- The cover plates and reed plates are attached with nails, not screws. You have to pry the nails off, and they're usually replaced with screws. 
- When you do this, it no longer seals well. To fix this, most people sand various pieces to improve the seal.
- more info from Andrew Zajac