I recently bought a Tascam 424mkii in great condition from ebay, but when it arrived it had the worst cigarette smell I’ve ever encountered. The poor thing must have sat in an unventilated space where smokers smoked for years.
What helped me was Sunlight, Fresh Air, Simple Green, and Baking Soda.
I set it by a window that gets lots of direct sunlight all day. I opened the windows. I must have left it there all day for a week.
While it was sunning, I took a damp cloth and sprinkled some Baking Soda on it, and then used that to carefully wipe all the surfaces of the machine. This left a grainy baking soda residue on the machine that I left on it for a couple days, since I figured that would help soak up some of the smell.
After sunning and baking sodaing, I used a damp cloth to wipe off the baking soda. I still had some smell coming from buttons, knobs, and other hard to clean spots. So I took some Q-Tips, dipped them in Simple Green, and cleaned every nook and cranny I could find. I ended up doing that multiple times.
After all that, my machine is now virtually smell-free.
In my case I was cleaning off that residue that gets left after years of smoking indoors. It sounds like you’re not dealing with that kind of odour, so maybe just some Baking Soda and Sunlight will do the trick?