rcsdiff in RCS version 5.7 seems broken (cygwin version)

Hello,

Yesterday, I (re)ran v 2.697 of Cygwin's setup.exe to update anything
that was out of date.

Among other things, it updated RCS.

After the update, the rcsdiff command no longer works on my box.  My box is
is:
     Dell Precision WorkStation 390 running Windows Vista Business (x64)
Service Pack 2

Here are the symptoms:
     $ rcsdiff test.txt
     ===================================================================
     RCS file: RCS/test.txt,v
     retrieving revision 1.1
     co: not found
     rcsdiff: RCS/test.txt,v: co failed

     $ echo $?
     2

2 == ENOENT / No such file or directory?

     $ ll test.txt RCS/test.txt,v
     -r--r--r--+ 1 rich None 242 2010-05-27 10:55 RCS/test.txt,v

*** n.b.,?ALL OTHER RCS COMMANDS WORK -- ci, co, rcsdiff, rlog, ...

Cygwin version is (ac. to the cygwin1.dll properties of "Product version
1007.5.0" and modification date of "4/12/2010 1:09 PM"):
     Version 1.7.5

RCS version is (this matches cygcheck.out "rcs 5.7-10"):
     $ rcs -V
     RCS version 5.7

Sizes and dates of rcs exes are:
     $ ls -ltr `which rcs co ci rcsdiff`
     -rwxr-xr-x 1 rich root 71K 2010-05-20 15:57 /usr/bin/rcs*
     -rwxr-xr-x 1 rich root 66K 2010-05-20 15:57 /usr/bin/co*
     -rwxr-xr-x 1 rich root 70K 2010-05-20 15:57 /usr/bin/ci*
     -rwxr-xr-x 1 rich root 48K 2010-05-20 15:57 /usr/bin/rcsdiff*

cygcheck.out is not attached but I can provide if needed.

Anyone else seen this?

-RD