vacuum brake unit leak???

My 2003 Ford Ranger loses brake vacuum after sitting a few hours. I called the dealer (it's still in warranty) and the service advisor gave me an astute, highly technical answer; he said "there's too much going on in there to hold vacuum". I don't remember losing vacuum during the first year and now it sometimes loses it in an hour or two. Also, I don't remember losing vacuum in any other vacuum boost system I've owned. Am I getting a snow job???