Getting Rid of Mildew Smells

Try steaming to clean, if you haven’t, and use a closet moisture absorber (the ones with beads) to suck all the smell out.

There might be an ongoing mildew issue. It sounds like you cleaned a lot but maybe you missed something? Headliner? Package tray? Visors? Headrests? Arm rests?

Short of getting those dampener removers, a sock with rice or those silica (do not eat) bags should absorb any humidity inside the car and kill off the mildew. Just leave them under your seat or where you suspect there’s moisture coming in.

Mildew happens when there’s moisture: Mildew - Wikipedia

Read the environmental section.

I had a white powdery mildew on my package tray cardboard so I steamed it and then hung a closet absorber in my rear seat (it had a lavender perfume which was obnoxious). The steamer cleaned it well. Wear a mask if you are sensitive to particles (I didn’t, and it was gross). I think it might have been a slow window seal leak in my car or just never cleaned. After the closet absorber drew all of the moisture out, my Dart sat and smelled better (like an old car). It filled the entire bag with water within a few days. I bought it at a Walmart and there’s a plastic hook. The beads are on the top section and the bottom one shows how much moisture it draws out. Mildew never came back and it didn’t smell stuffy. After the first bag, I put in another and it didn’t catch any humidity. A few years after, and sitting around, and it’s still not back and smells ok.