Another possibility is the aluminum casting could be cracked. If the engine was removed at some point in the past and the mechanic did not remove the oil filter, very often the filter hits the cross member. These filters are very long and act as a long lever arm. This coupled with the heavy weight of the engine dramatically increase potential for damage to the filter casting. Since the process of removing and resealing the cooler is messy, time consuming, and costly it may be wise to consider replacing the casting.