I sincerely doubt that leakage will be a problem with any modern ammunition. Hand loaded or not. The swaging effect of pressing the primer and bullet into the case will give you a far more effective seal than anything you could add.
The so called sealants we sometimes see on milsurp ammunition, isn't a sealant. It's there to keep the bullets in place under harsh conditions, that may create internal gasses and high heat from rapid fire. Remember, anything you seal the cartridge with, around the bullet and case neck area, will increase pressures. Probably not a real problem in most case scenarios but if you're loading to near max pressures already, could easily be a cause of case failure.
I have a hundred or so 1930s dated 303Brit that I found at the bottom of a well. That was in the late 60s, so they were there for at least 10 years before I found them. That's how long we owned the place before hand. They were covered in grime but cleaned up like new. Apparently, in deeper water corrosion isn't much of a factor. There were also several dozen bottles of beer as well. The lables were still intact and the caps had a bit of rust but that's it. The beer was skunky but clear.
Those cartridges all hang fire. Not because of moisture intrusion though but because of primer deterioration. I suspect that's why they were down there in the first place. The well is long gone by the way. It was wooden cribbed and deteriorating. That's why we explored it in the first place. I know this stuff is off topic but the fact that the ammunition was submerged for that length of time and still dry inside is relavent.