Thanks….. certainly could be an old spill. It’s been like this since I bought it a year ago. It was a rental, so God knows what had happened. I had a tbird a few years back that had mice nesting in the hardtop – between the outer shell and the headliner. Horrible smell, I had to replace the headliner. With that in mind, I spent a good hour in the Mustang the other day looking in every crevice under the seats, under the dash, in the vents, between the canvas top and the headliner. Also replaced the cabin filter. No indication of rodents. So I’m back to fabric seats and/or rug. I bought a nice portable rug cleaner – I’ll scrub the interior again.