Rebuild, refurb, or new

So since I bought my 05 4.0 manual with 119k mi. a year ago, 1st going into 2nd has always been temperamental. Sometimes it buzzes but still goes in fine, other days I don't hear a thing and shifts are more or less clean. I know its the synchros, so Im considering getting ahead of it. I plan on a flush sometime soon, but what would you do for a permanant fix and consider the most cost effective?