My GTX sat from 1982 until I bought it - same issue. Mice made a hotel in the headliner.
I replaced both the headliner and carpet, washed the vinyl seats and trim panels three times with Dawn dish soap and a soft bristle brush. Let them set out in the sun until dry each time. Soaked the backsides each time with Fabreze.

Spray dyed the plastic kick panels and seat back.

Smells like a new car.

Side note. I had a rental that had cats and dogs that messed the basement up. I tried everything to get rid of the stench.

Tried for weeks. Vinegar and baking soda in two days and the stench was gone.