I just spent two weeks struggling with this sync bug. I found this thread and followed the steps suggested by Jeremy Garchow (delete audio track, easy setup to 23.98, then re-import audio) however, after following the steps my FCP sequence was still out of sync.
I was running FCP version 6.0.5 and my operating system was 10.4.
I just updated FCP to version 7.0 and also updated to snow leopard and everything syncs up perfectly.