What is the primary indicator that a rear shock absorber has failed internally and needs to be replaced?

1. Oil leaking down the damper rod body, and excessive bouncing of the rear suspension after hitting a bump.
2. The chain slack increasing by more than 10 mm when a rider sits on the seat.
3. The rear brake pedal sticking in the depressed position.
4. A loud whistling noise coming from the exhaust muffler.