Further to Whale’s excellent response, it is evident here that the owner’s letting agent is not doing a thorough job, if it cannot be determined which tenant was responsible for the damage. A condition report should be made out prior to and immediately after each lease of the property, this would have determined which tenant was responsible. Tenants are required under the terms of their lease to be responsible for any damage to the property as a result of their negligence. A bond is collected from tenants, the cost of repair can be deducted from their refund at the conclusion of their lease.
I’ve had similar damage done to a garage door (common property) by a tenant of mine, it wasn’t reported to me and only became evident at the time the tenant vacated. As a proper inspection was done by my letting agent, the cost of repair was deducted from the bond. In this case, I’d highly recommend that the owner concerned be advised by the OC that he/she should seek a more diligent letting agent if he/she doesn’t want to wear the cost of damage to common property by a tenant. 