Tilt/slide seat doesn't

On our 2004 Suburban the Tilt/Slide seat (by the rear passenger side door) no longer slides forward when the back is tilted, making entry to the third row more tedious. The seatback still latches/unlatches properly, and it can still be folded flat, as in older Suburbans . . .the problem with that is Mrs. Kid is tall, so the front passenger seat is usually too far back to allow the seat in question to be folded flat without a collision between teh lower cusion of the back seat and the back of the front seat. This is making the school drop-off zone drill rather complicated. Before I turn the amatures at the local dealership loose on it again (they've seen my Suburban 3 times, each time they've fixed one problem they've caused one or two more, which I've fixed myself because it is SOOO hard to live without the Suburban), I thought I see if any of you have the secret to getting it moving again.