The way in which point defects interact with grain boundaries in oxides is important for understanding radiation damage evolution, sintering, and many other technologically important applications. Here, we examine how vacancies interact with three different grain boundaries in MgO, chosen as a model oxide ceramic. Further, we compare the vacancy interaction with both pristine (as constructed) and 'damaged' boundaries, in which excess interstitials are placed in the boundary plane to mimic the structure after a damage event. We find that the excess interstitials significantly change the interaction of the vacancies with the boundaries and that this change is sensitive to the atomic structure of the boundary. We further observe that complex electrostatic effects arise that can dominate the interaction. These results show that, as boundaries absorb defects, their interaction with other defects will change dramatically.