Chemist speak time.....Most of the oils in horn lubes contain long chain unsaturated hydrocarbons and these are able to partially oxidize and give the "rancid" smell. Being the chemist, I decided to push the oxidation reaction the rest of the way and sprung for a small ozonizer off eBay....the kind they sell for getting rid of cigarette smell in hotel rooms...about $90 from many sites. I put the case inside a large trash bag with the ozone generator able to blow into the bag and let it do it's thing for two days. Then pulled the case closed while still in the bag and allowed the O3 (ozone) to hang out in there a couple of days with the case closed and the generator off during a business trip. After a thorough airing out of the case on the one day in the past 6 months where we've had sun here in Seattle, most of the smell was/is gone. When I was in graduate school, we called this approach to solving a problem "the brute force approach" as contrasted to an "elegant" one...However, if you smelled the case that came with my '30's Artist Bore HN White Silvertone you would have said it needed "BRUTE FORCE APPROACH" on steroids. This took care of most of it. I've also had good luck with a product called Mirazyme from McNett before going to the ozone because I don't like dissolving the old glues used to hold the felt lining in the case. Mirazyme is used to take the stink out of diving we suits where I hear one of the ways to keep warm is supposedly to urinate inside the wetsuit. Never done that but the stuff takes stink out of my old tents and if it works on wetsuits I figured it might work good on a case.