check the shaft that connects the seat motors. the end piece that holds them together sometimes can come apart, but can be fixed with a little persuasion. If just one of the shafts falls out / breaks it'll still pull the seat forward but not have the juice to push it back on the two screws. Easiest way to do this is to pull the seat out. This is whats happened to mine before, but it could be the motors burnt out or something else.
1997 SC300 LSx Powered
1997 LX450 Locked x3, ARB winch bumper with warn, 4x4 Innovation Sliders, 850/860 springs, man a fre front coilspacer. Cooper STT 325/80/16s, rear slide out storage