Yes, they will seal up just fine as long as your bottle and cap threads do not get paint on them. I have had most of my 23ml jars for many years. Of course some colors such as Flat Black, Dark Yellow, Flat White, etc. dont last as long due to high usage. I have never had a bottle of Tamiya paint dry out on me. Even those that got a bit thick were revived with distilled water. Overall quality control has never been a problem there.