Hello,  I rebuilt an Otto-Higel action about 25 years ago, (I can't
believe it's been that long).  I remember it vividly, however.

The most unique thing about this one are the pouches.  Instead of the
typical leather disk set into a well built decks or valve blocks,
or whatever, (depending on the brand), the Otto Higel uses tiny
"unit pouch blocks", for lack of a better term.  They are rectangular
and have a short piece of internal tubing that directly leads them to
the tracker bar via a brass nipple built into the valve chest.  The
pouch blocks are held in pairs by a leaf-spring clamp tightened by
a wood screw.

Be sure to replace the pouch leather with the thinnest and highest
quality you can find.  Because of their shape and size they will need
to be exceptionally flexible in order to be responsive to fast
repeating notes.  Don't stretch the pouches when you glue them, again
leave them flexible, (but not overly baggy).  The valves are ridged and
speared over a center pin.  The new valve leather needs to be thin but
smooth and able to make a tight seal.

The valve chest itself is huge in order to accommodate all these
internal parts and the cover and internal sides should be well sealed
with shellac before reassembling.  The entire back surface of the unit
pouch deck is covered with pouch leather that will need replacement due
to invisible leakage.

I removed the old material with a blowtorch which must constantly be
in movement so not to burn the wood.  Scrape any remaining glue off and
sand it smooth.  Replacing all this pouch leather will be expensive but
must be done.

Some skill will be required to accurately replace the valve block guide
pins.  Use new piano action center pins for their replacement.  Overall
there is nothing unusually difficult about rebuilding the Otto-Higel
player but it will get you scratching your head with a resounding "wow"
when you get huge gasketed cover off.

I'm not certain what you mean when you refer to "a few of the
key-bellows stay closed" but I must assume you are referring to the key
striker pneumatics.  There are no internal springs.  If this is your
first rebuild you must understand that the pneumatics are one of your
primary and most involved tasks of the project.  Every one of these
will need to be removed, the old rotten cloth removed, cleaned, and
then replaced with new pneumatic cloth, no exception.

The same goes for _every_ pneumatic, every gasket, every pouch, every
valve facing, etc., etc., etc., all redone using hot hide glue.  It
will all be rotten and leaky.  If you don't have it already, you must
purchase the Reblitz book, "Player Piano Servicing & Rebuilding," and
read it cover to cover before picking up a screwdriver.  It includes
a few paragraphs and pictures of the Otto-Higel player.

I understand several different types of tracker systems were used
On these.  The one that I rebuilt was mechanical, (as opposed to
pneumatic), and worked impressively well.  The one problem with this
that I encountered, however, is that the teeth on one of the gears that
operates the friction wheel had completely worn down.  What's worse is
one of the tiny end center pins that hold it in place had broken off.
I had to locate someone who rebuilds antique clocks to fabricate me
a new one.

On the tracker bar, the little springs inside the roll edge feelers had
also broken.  I replaced them with modified hammer return springs which
worked beautifully.  Once I finished completely rebuilding the player
action as well as the piano action, restrung the piano, and refinished
the case, the piano played and sounded very nice.

Good luck,
Rob Goodale, RPT
Las Vegas, Nevada