This is only through my experience, i dont like smoking oil (i find it hard on my lungs/chest) and a few months ago i got a deal on it, anyways its been sitting there since christmas time and i take some it and it looks fine (its a larger amount not just a little vial full).
Im going to assume that if ur using alchoal (99 iso) you would kill alot more of anything on it if there is anything on it then with butane. However i think this leads to making diffferent weed things