You could try selenium toning the negative. THis will add density, but NO DETAIL. Might help with the printing adds about 1 grade of contrast.
Selenium 1:2 soak for about 5 minutes. Some people use water, others HCA.
Ansel Adams in "THe Negative" recommends the following
soak negative thoroughly in water the re-fix for several minutes in PLAIN hyo. Place in selenium diluted with HCA for about 5 minutes. Follow with a plain HCA and washing as usual. He also suggest that you test the procedure first with a discarded negative of the same emulsion.
Steve Anchell suggest that if you are sure that your negatives have been thoroughly washed, and you have not used a fixer with a hardenerm then refixing should not be necessary. "But when in doubt, refix."
Photography Formulary also carriers an intensifier, but I have not tried their version.