The links fall off when the end of #1 bends upward and it's being forced into reverse. You could bend it back or buy the current part# 9800898780. Reverse is a straight cut gear and you need to let it drop in, not jammed in. From memory, bracket #4 was modified slightly (was 241133 now 9800899080) to make it less likely the links can fall off. The 2 x short links are part# 2454E9 and if they pop off the balls easily, replace them.
