Mike,

If the glue is hide glue, I know folks who use a few drops of vinegar to 
revitalize glue joins in wooden clock movements.
Warning, I haven't actually tried this but can see in theory how it 
might help.
That said I suspect such a repair is temporary, especially in a highly 
loaded structure such as your chair.

Probably the best long term solution is to do as suggested earlier, 
break it apart and re glue.

Troy