Your dealer is full of Bull S*** and some cars built before Dec 31, 2003 are prone to this problem. It's a well known and documented fact. The early fix was to swap out the transmission. Now they open it up to replace syncros. There have been some cars that still required a tranny swap to fix the problem.

Yes, it is extremely hard for them to duplicate as you never know when it will happen. Stick by your guns and get it fixed.