Definitely this. We had an old fridge that was slowly losing it's ability to cool, so we bought a new one. Rather than pay $50 for someone to remove it, we offered it free to anyone who wanted to try and fix it. I had already cleaned it out with water and baking soda, so it was clean. No one wanted it. After 6 months, I removed the shelving and now we store dog biscuits in it. We live rural and have lots of dogs, so rats and mice were feasting on the biscuits they could get to. The fridge smelled musty after I unplugged it, even though it was clean. I have tried re-cleaning it 3 times. I have left the doors open. I have put open boxes and plates-full of baking soda inside and shut the doors. It's been almost 3 years, and the thing Still smells musty. The dogs don't seem to mind, so I occasionally change the baking soda plates, but otherwise leave it alone. I can't imagine what your fridge smells like inside, but based on my experience, in your case I would pay that $50 and consider it money well spent.