Hi Al,  The cracked sound board on your Stella would certainly have an
effect on the sound volume and the tone.

A more important problem might be the sound post.  This is a wooden
post that touches between the bottom of the bed plate near the combs
and the sound board.  Sometimes the sound post is a simple piece of wood
and sometimes it is an adjustable jack post.  That is, it's a threaded
dowel and a wooden post that is threaded internally so that they can be
put in place and then "unscrewed" so that they fit tightly between the
bedplate and the soundboard.  I haven't looked inside a Stella in
several years but I know the Mira's have a threaded post.  Stellas and
Miras were made by the same company.

Third is the excessive oil.  The only things on a disk box that should
be oiled are the pivots on the shafts of the spring motor and a tiny
bit on the starwheels.  (The spring and the worm need appropriate
grease.) Oil on the combs is a no-no.  Oil or grease between the teeth
and/or the weights will dampen the vibration and reduce the sound.  If
you don't have experience restoring a music box, you might want to call
someone who has for advice - it is rather easy to damage the box or
yourself in the process.

Regards
Craig Smith - finally snow in western New York

P.S.: By the way, a very thin film of oil on the back of the disks is
also a good idea to prevent jamming a starwheel down into the lower
comb.  And do not play a disk if it is rusty.