Leather treatments usually contain some combination of the following components:

Small amounts of:
* Formaldehyde
* Methanoic Acid
* Methanol
Larger amounts of:
* Glycerin
* Ethyl Alcohol
* Isopropyl Alcohol

Plus whatever byproducts of the particular tanning process used to produce the leather haven't been washed out.

I personally like the way glycerin smells on leather, but I'm not sure if that's the "used european car smell" you speak of!