To protect your RC paper prints to the highest level of certainty currently available, make sure they are fixed and washed correctly then use Sistan in accordance with it's instructions. It might be available from other manufacturers these days (I just checked, it is now called AG-Stab) but that will do the job. Selenium toning has to be a total replacement of the silver to give complete protection, and that will change the image appearance.
Dumb question, but is this stuff OK/recommended for use on negatives? I'm about out of PhotoFlo and noticed it has a wetting agent included... I'm tight on space to the fewer the bottles of concentrate I have laying around the better.
New-ish convert to film.
Pentax MX for 35mm
Bronica ETRS for 645