Removing the Odor of Spoiled Food from Car?

I was helping a friend out a few years back and transported posole to a fund raiser and though we tried to level the trays, the juices spilled onto back seat and also in the space between where the back meets the seat. I've had the car detailed and the seats and rugs cleaned a few different times, but anytime the weather is damp or I run the car through a car wash, I get this awful, sour smell.

It is similar to when I've let a meat dish go past bad to "oh my word" in the fridge. My fear is there is nothing that can be done since the part that I assume needs to be cleaned is out of reach unless there is some way to remove the back seats. Any ideas are welcome!

By Donna B.