I've just been through this process with an old case that smelt mouldy/ musty.
Febreeze was a misstep in my case (excuse the pun), although anecdotally others have had success. I felt it made it worse (like spraying deodoriser to disguise bad toilet smells), but it's quite likely I executed it poorly. The only thing that worked was a combination of judicious vacuuming of the insides and exposure to direct sunlight/ airing in my garage.
I realise this doesn't help you much, but I didn't think the smell would ever go and it's completely tolerable now after a concerted effort.