"补铸件的漏洞" can be translated as "repair the leaks/defects in the casting" or "patch up the holes/flaws in the cast part".
Here, "repair" or "patch up" convey the action of fixing, while "leaks/defects" or "holes/flaws" refer to the issues in the casting that need to be addressed. The choice of words may vary slightly depending on the specific context and the nature of the "漏洞" (leaks/defects/holes/flaws) in question.