Fluid was seen on the ground around the right main gear after the aircraft parked. The head of a bolt on the shock-absorber on the right main gear leg was missing and there was a small puncture in the right main gear door. During the subsequent investigation it was concluded that the bolt had fractured due to fatigue, and the bolt had exceeded its 18,100 landing fatigue-life limit. The design of the shock-absorber is such that the small loss of oil does not cause a significant degradation in aircraft performance. At the time of the occurrence the operator was not monitoring the life of these bolts, but has since changed its procedures.