Why seal the primer and or neck of the case? No reason unless one or the other or both leak. For long term storage of loaded ammo the need for a good seal is against atmospheric changes. Before I seal the primer and or neck of the case I will load the ammo, heat up a 30 cal. 20mm ammo can then load the ammo (neatly) in the can then shut the lid with the cam over latch, label it and then wait for the atmosphere in side the can to cool, then forget the effect time takes on on everything inside the can. Same for pistols, lube, wrap, heat the can, load the can, close the lid and it is done.
Testing ammo for leaks: I have no shortage of vacuum pumps or wide mouth gallon jars, just modify the lid, fill with loaded ammo (test group), finish filling with water, place vacuum on jar then watch for bubbles, if you are busy and do not have time to watch, load ammo without powder, place a vacuum on the jar, then later pull the bullets and check for water.
It is not likely the reloader knows the total weight of the components in each round loaded, but on the outside chance the weight is known the reloader could, after removing from the vacuum test jar, weigh the ammo again to determine if the case took on any water.
It beats talking about something that may never happen, Electrolysis is the bigger problem of the two with the different metals used in ammo, still reducing the moisture in the atmosphere reduces electrolyses.
Or load the can only on dry days.
F. Guffey