There is one simple rule, which you accepted when you temporarily imported your Subaru:
You CAN NOT sell your US Plated car TO A MEXICAN, OR ANYONE ELSE IN MEXICO.
OK, Now that I have your attention, I hope I'll save you a lot of legal heartache. You can't even let a Mexican drive your car without you being in the passenger seat; not even a valet. There are strict laws that you must be aware of. One of the most important is that you have agreed and posted a bond to insure that YOU will remove your car from Mexico. You have to do that and sell it in the USA, not in Mexico. WHENEVER, you leave Mexico, be sure to stop at 'Aduana' and get the import sticker removed AND get the receipt. Even if a customs agent says you don't need to, if you are returning, he is wrong and you can really end up in a mess if you can't bring the car back to remove it legally. So, insist.
If the car were manufactured in a NAFTA country, you might be able to import it permanently, but it is difficult, very expensive and a big hassle, seldom worth the trouble.
There are real horror stories that have happened to people who have violated these rules.