If your oil cooler is starting to come apart, you have two choices. The first is to have it replaced. The second is to have a competent radiator shop take a look at it to assess the possibility of repair. Keep in mind that even if repaired, it is likely that it may degrade further in the future. Flowable epoxy is like JB weld. It would require operating room cleanliness for the cooler prep and a huge amount to seal the base of the tubes. But, as you know, the oil cooler runs at system oil pressure. Save the headaches and get a new one. BTW which car?
1987 BMW 325