A tenant may not deduct pursuant to this section an amount greater than four months' rent in any twelve-month period, or period of occupancy, whichever is shorter, from rent due to the owner. Such amount shall be computed on the basis of the highest monthly rent during the tenant's occupancy or during the twelve-month period before the violation is repaired, whichever is shorter. Where the violation affects more than one unit of a multi-unit structure, or a portion of the structure reserved for the common use of tenants, the amount deducted for repairs for all affected tenants shall not exceed the total of four months' rent due to the owner from all affected tenants. Failure to exercise any rights under this section in any twelve-month period shall not increase a tenant's rights in any subsequent twelve-month period.