car wont shift into 6th- is this common?

[aj1082]

My Firebird Formula WS6 '97 won't go into 6th gear anymore. The dealership says its prob the synchronizer, but one of my firneds said he's heard about it before, and the problem is a simple fix. If anyones heard about this problem unrelated to the synchronizer, let me know. There were only around 400 of my cars made- so im hoping its a simple fix.