I pulled apart a faulty back once and fixed a problem - a sort of ratchet system tooth had sheared off so I filed a new one - worked well for another year but now its a little crunchy and on one occasion didn't fully wind a frame - I no longer use it, but may well open it up again for a look-see

As for lenses - scary business, I would like to be able to get some compressed air in there to clean up the dust tho (:

good luck to ya