When we pulled my '38 out of the barn where she'd rested for over 20 years I discovered that it had been the home and potty for tiny creatures too. As you discovered it's impossible to get into every nook and cranny. I cleaned the best I could but still had some smell, especially in the summer. It took a couple of years but the smell eventually fades. The only way I know to eliminate it completely is to do a body off & dip the body.

Save a life, adopt a senior shelter pet.
The three main causes of blindness: Cataracts, Politics, Religion.
Name your dog Naked so you can walk Naked in the park.