Once you have the bowl/valve seat area clean the easy check is to spray liberally with Brake parts cleaner,then blow and watch the area your checking. The BPC will dry way fast on the surface but you'll see cracks as the fluid slowly evaporates from the cracks . Yep,Learned that trick years ago for cheap fluxing of TAFC cranks between rounds. this will not find a very minor crack but if the cracks go to water the chamber will be very clean and nothing like the chambers next door. Most magnum heads are cracked.