This previous
thread discusses the selenium issue.
Looks like the votes are about evenly split between replace vs. leave alone. FWIW, the previous owner of my CT-100 did replace the seleniums. If you replace 'em, disconnect the old unit completely (that is, don't wire the diode in parallel).
Regards,
Phil Nelson
Phil's Old Radios
http://antiqueradio.org/index.html