They didnt come with a sealant from factory. If the surfaces have been linished or damaged then you can use one.
In anycase, I do use a sealer,Permatex Aviation" cement.
Use sparingly and if possible leave a 1 mm gap on the inner for expansion, although minor spill will not harm the engine as it does not dry.
Clean up the outer casing with turps.
This will give one of the best seals for non gasket applications.
Do not use Silicone, as over spill can break off into the engine.
