The Importance of keeping the oil sealed is to maintain sterility. You want to deff store the oil in a sterile enviorment. If you need a source for multi-use vials just PM me.
But if all you have is syringes and your ready to use the stuff now is just keep what you have left over in the syringe then just switch needles out each time you inject.
But with this way their is to much room for error, so me personally I would just get a sterile vial and keep it in there.
Hope this is some what helpful.