Check the shock-absorber on existence of damages and leakage of oil.
Check, whether there are no traces of damages or wear on the rubber plug.
Put forward and drown a shock-absorber rod not less than three times. Be convinced that force of resistance does not change and there is no unusual noise.
If it not so, replace the shock-absorber.
Drown a rod of the shock-absorber and release it.
Be convinced of that the rod is put forward completely with normal speed.