This is the reason I disassembled the GPS. After using it this long, I was suddenly not able to turn it on and off. The On/Off button is on the side of the GPS as shown. The hard rubber piece had cracked inside the unit. Because it was split, it would not press the On/Off button on the main circuit board.

You can see the small cracked rubber piece, setting on the table. I can reach in with a screwdriver and press the internal button. I haven't figured out a piece to put in place of the cracked rubber. Maybe I need a 3D printer.