Many thanks to those of you who responded off line -- the answers were
interesting and varied.  I'd encourage folks to reply to MMD as well to
help build this resource.

There was about a 50/50 split on using cloth vs. leather for a foot
pumper.  The argument for cloth being to keep it the way it was
originally, and that there is good cloth currently available.  The
argument for leather being that the quality and likely life span is
better.

Pretty much everyone who supported cloth referred to using "Haartz
cloth", a material made a couple miles from my house, primarily for
replacement convertible tops.  Investigating their web site I found a
bewildering array of cloth types and styles, many with synthetic cloth
backing that may or may not adhere with hide glue, my preferred
attachment method.

I spoke with the very helpful technical rep at Haartz, who was
surprisingly familiar with use of their material in pianos and organs.
He told me that the prior material called Cambrio had been
discontinued, but a different product called Stayfast had replaced it,
with the only difference being a black vs. white cotton lining. He said
that other than color the products were identical.  Apparently this is
now the only product Haartz makes with a non-synthetic, cotton backing.
See http://www.haartz.com/products/stayfast

This cloth (Haartz part # 5750014A for black) is available retail by
mail order from the Miami Corporation of Cincinnati, Ohio, and may well
be the cloth sold by different rebuilding suppliers.

In 20 or 30 years I'll let you know how it works out.

Roger Wiegand
Wayland, Massachusetts, USA
http://www.carouselorgan.com/