1. Lost.
2. Rubber aged and cracked causing it fell off form the frame after long period of time.
3. Rubber aged and contain foreign substances.
Suggest to replace wiper blade or wiper blade rubber.
1. Dismantle the wiper blade.
2. Use a towel to wrap the wiper arm to prevent the wiper arm retract and hit the windshield glass.
3. Replace with new wiper blade or wiper blade rubber immediately.