The skills required for repairing and restoring most old Fountain Pens can be acquired quite easily. The replacement of ink sacs is normally not difficult and the sacs themselves are readily available, if you know where to buy them. Lever fillers are to best to start learning on as the are normally the simplest mechanisms.
A great deal of satisfaction can be gained from restoring what might now be just an attractive ornament (for this is all a non-functional fountain pen can be) back to a fully functional writing instrument, probably with a bit of style and history.
I would advise you on a few things if you want to attempt any repairs yourself:
I have listed below suggested sources of knowledge and parts that you may wish to use if you decide that you would like to repair and restore your own fountain pens.
Arthur Twydle, The Pen Museum: Pen repairs, spares, tools, books, videos and workshop on repairs
Jim Marshall, The Pen & Pencil Gallery: Pen repairs, spares, tools, books and videos on repairs
The Battersea Pen Home: Repairs and spares
David Wells: Repairs (all profits to the Cystic Fibrosis Trust)