Apart from creating an ls-R file I am not sure what is wrong. Did texinfo.tex actually get installed under /usr/local/share/texmf/tex/texinfo?
To create the ls-R file try "mktexlsr /usr/local/share/texmf". I don't understand why it is not working for you as you have managed to use new versions of texinfo.tex before. If all else fails you could copy texinfo.tex to the same directory as your manual.
