Hello, Serge,  I'm Bob Loesch, from northern California, USA, and
I used to run a clock shop called "Cuckoobob's Clocks", specializing
in cuckoos of all sorts and ages.

Although I never worked on a flute clock myself, I have seen many and
I did a restoration of the reed portion of a Wehrle trumpeter clock
some years ago.  The actions of a trumpeter musical movement and a
flute clock are quite similar, differing mostly in the type of organ
pipe used.  Also, I've  been a pipe organ owner and serviceman for
a bit over 40 years (specializing in theatre pipe organs), so I feel
qualified to speak on this subject.

My advice to you on this wonderful Black Forest clock would be to first
completely restore the clock movement and case, such that when restored
it can be reinstalled in the case to protect the movement.

The bellows and reservoir for the flute pipes should be covered with
some sort of tough airtight leather, like a split cowhide or kangaroo.
Pay attention to any stiffeners on the inside of the bellows.  Needless
to say, gasketing is paramount, as these tiny pipes usually run on very
low pressure, so any leaks will keep them from speaking properly.

Valve pallets are normally covered with white goatskin or similar very
soft but airtight leather.  Pay close attention to the thickness of all
gaskets and sealing surfaces, as often the clearance they provide is
critical to the movement's proper operation.

Please avoid rubber cloth (unless used originally) and other modern
"wonder products", as they usually don't last as long as claimed, and
often require modern, specialized glues that are difficult to clean up,
and almost impossible for the next repairman to remove.

Most importantly, _please_ use _only_ the original hot hide glue, from
a glue pot!  I've seen many clocks, organs, player pianos, and other
player instruments ruined by the use of modern glues of all types from
"white glue" to epoxies!   The original hot hide glue will last as long
or longer than the other original materials used in the restoration,
and the use of hide glue insures that any future restorations may be
done with no damage to the old wood.

If you can locate a pipe organ serviceman in your area, you may be able
to show him the mechanism and get his advice firsthand, which is
difficult to do by "remote control".

I'm happy to answer any more specific questions, and I'd love to see
pictures of the clock, sent to my email above.

Good luck, and happy New Year!
Cuckoobob - Bob Loesch