"General Dynamics began delivering the new LAV-AD to Marine light armor units in the fall of 1997."
http://www.fas.org/man/dod-101/sys/land/lav-ad.htm
another source---
http://www.nationaldefensemagazine.o...rine_Corps.htm
says....
LAV-AD, fielded in 1999, with Stinger missiles and a 25 mm Gatling gun to provide air-defense protection for forward elements.
so it looks like is was delivered in late 1997 may have been fully operational in 1999 and up 'till then the Duster would have been the unit in service
Don