The ground glass stoppers on bottles will provide a perfect seal as long as they are greased.
Silicone grease should be smeared fairly liberally around the ground glass part of the stopper so that when inserted in the bottle neck it spreads to form a seal. It is not necessary to apply any force to the stopper when inserting into the bottle. In fact if properly greased the stopper can simply be dropped back in place, making it a fast and efficient container for your oils. Grease will also prevent stoppers becoming bonded to the bottle by raw materials that form sticky or resinous deposits. Silicone grease will not effect perfume ingredients.
It may be necessary to re-grease your bottle stoppers occasionally depending on usage.