Ordinarily tcsh-6.08.00-5 works fine. However, if I su and then invoke /bin/tcsh, the $shell shell variable gets set to /usr/bin/tcsh which is non-existent. This also shows up in a strings of the binary. FWIW, on other RH boxes to which I have access tcsh-rhcn-6.08.00-1 gets its own path right.
Fixed in 6.08.00-6. Thanks!