Fixing a pendant capsule HELP!!!

[ex-miss-adda231.livejournal.com]

Ok I got this as a gift last year...  I noticed that the cap started to come loose, and now I am wondering....  Can I replace whatever fluid is inside?  Does anyone know what they use?  It is smells like some sort of oil...  But I am not sure!  I have lost a bit of the fluid, and now I don't feel that there is enough in the capsule.  I am going to hot glue it shut once I figure out...  Here is a pic of it I am quite sure a lot of you have seen these!