Can an old cedar closet block become effective again if you spray it with cedar oil? I've been doing this, but I really can't tell if the bug-prevention is really being reactivated. I don't know how often to do it, either. They really don't smell cedar-y for more than a day or two after spray even though I use a lot of oil. Do I just have to buy new blocks? Should I spray the oil on some other material? I don't like mothballs and much prefer the cedar smell.