Clearly the garbage I have encountered was a brushed on product.
Craig Brougher pointed out this was likely neatsfoot oil.  It clearly
was applied by a brush.  If silicon grease is the tried and true for
over 40 years, have at it.

The old timers often "painted" porous pouches and ventils with egg
white.  Obviously a silicon product would last longer.  I do not work
with vacuum instruments -- and I do not want any part of working on
them.  I enjoy their music.  In pipe organ work, I can see little value
in silicon grease on leather and never the use of oils on the leather
as used in a pipe organ.

Tom DeLay
Salinas, California